AI Trajectory

null

{
  "Introduced": false,
  "Reasoning": "The crash report is a hung task warning (\"task syz.2.1137:10687 blocked for more than 143 seconds\") where task 10687 is blocked in `down_write()` within `fuse_file_fallocate()` called via `madvise(..., MADV_REMOVE)`. The lock it is waiting for is the inode rwsem (`\u0026sb-\u003es_type-\u003ei_mutex_key#31`), which is held by task 10683 executing `fuse_file_write_iter()`. This is a known condition during FUSE fuzzing where FUSE filesystem operations block waiting for responses from the userspace FUSE daemon or become deadlocked.\n\nThe patch series under test only modifies kernel virtual memory mapping/unmapping error-handling logic (`mm/vmalloc.c`, `mm/kmsan/*`, `mm/percpu-vm.c`, and `arch/powerpc/*`). It does not modify FUSE, VFS fallocate/write paths, madvise, or rwsem locking. Therefore, this hung task is completely unrelated to the patch series."
}

null

{
  "DiffStat": "arch/powerpc/kernel/isa-bridge.c |   5 +-\n arch/powerpc/kernel/pci_64.c     |   4 +-\n include/linux/kmsan.h            |   8 ++-\n mm/kmsan/hooks.c                 |  21 ++++---\n mm/kmsan/shadow.c                |   9 ++-\n mm/percpu-vm.c                   |   5 +-\n mm/vmalloc.c                     | 126 ++++++++++++++++++++++++++++-----------\n mm/vmalloc.h                     |   6 +-\n 8 files changed, 128 insertions(+), 56 deletions(-)",
  "HasCover": false,
  "PatchCount": 10,
  "PatchList": "The patch series contains 10 patches:\n[1] [PATCH v3 01/10] mm/kmsan: undo the shadow mapping when the origin mapping fails\n[2] [PATCH v3 02/10] mm/kmsan: skip vunmap_range_noflush when KMSAN is disabled\n[3] [PATCH v3 03/10] mm/vmalloc: clamp an unaligned range in vunmap_pte_range()\n[4] [PATCH v3 04/10] mm/vmalloc: propagate errors in vmap_pages_p*d_range()\n[5] [PATCH v3 05/10] mm/vmalloc: reject an unaligned range in vmap_pages_pte_range()\n[6] [PATCH v3 06/10] mm/vmalloc: reject empty and unaligned ranges in __vmap_pages_range_noflush()\n[7] [PATCH v3 07/10] mm/vmalloc: only flush the cache after the vmap succeeded\n[8] [PATCH v3 08/10] mm/vmalloc: undo partial mappings inside the mapping functions\n[9] [PATCH v3 09/10] powerpc: drop redundant unmaps of failed vmap mappings\n[10] [PATCH v3 10/10] mm/percpu: stop unmapping the CPU that failed to map"
}

core

null

{
  "Introduced": false,
  "Reasoning": "The crash report is a hung task warning (\"task syz.2.1137:10687 blocked for more than 143 seconds\") where task 10687 is blocked in `down_write()` within `fuse_file_fallocate()` called via `madvise(..., MADV_REMOVE)`. The lock it is waiting for is the inode rwsem (`\u0026sb-\u003es_type-\u003ei_mutex_key#31`), which is held by task 10683 executing `fuse_file_write_iter()`. This is a known condition during FUSE fuzzing where FUSE filesystem operations block waiting for responses from the userspace FUSE daemon or become deadlocked.\n\nThe patch series under test only modifies kernel virtual memory mapping/unmapping error-handling logic (`mm/vmalloc.c`, `mm/kmsan/*`, `mm/percpu-vm.c`, and `arch/powerpc/*`). It does not modify FUSE, VFS fallocate/write paths, madvise, or rwsem locking. Therefore, this hung task is completely unrelated to the patch series."
}

You are an expert Linux kernel maintainer and security engineer specializing
in crash triage and root-cause analysis.
Your job is to review a kernel crash report (finding) and determine if it was introduced / caused
by the patch series being tested, or if it is a pre-existing / unrelated bug.

IMPORTANT: The entire patch series has ALREADY been applied and committed as a single squashed commit
at HEAD (or on top of the base commit) in your workspace.
Do NOT rely on your internal knowledge of the kernel. You must actively use your tools to examine
the source code, inspect workspace diffs, and confirm any assumptions.

Available Tools:
- git-show: View the squashed patch series commit or historical commits. Call with Commit="HEAD" (default)
  and optional 'File' parameter to restrict the diff to a specific file or directory, or 'Stat=true' for a diffstat.
- series-patches: Browse the original patch series. Call without arguments to list all patch titles,
  or PatchNum=<N> to view the full description and diff of a specific patch (or cover letter, if present).
- read-file & codesearch-dir-index: Read exact source code files and directory contents in the workspace.
- grepper: Regex search across files in the workspace (git grep).
- git-blame: Inspect line authorship and find which commit last modified specific lines of code.

Triage Procedure:
1. Analyze the Crash Report:
   - Identify the crash type (e.g. NULL dereference, KASAN use-after-free, out-of-bounds read/write,
     assertion failure, deadlock).
   - Carefully examine the stack trace(s) — both the faulting call stack and, if applicable (e.g., KASAN UAF),
     the allocation and free stacks.
   - Note the faulting function, file name, line numbers, and the specific variables or data structures involved.

2. Inspect Workspace Changes & Patch Series:
   - Check if any files or functions from the stack trace appear in the modified files overview or the patch series.
   - Use git-show with Commit="HEAD" and 'File' to inspect the exact diffs for relevant files
     in the squashed commit.
   - If needed, use series-patches with PatchNum=<N> to inspect the author's commit description
     and rationale for individual patches in the series.
   - Use read-file to inspect the actual source code at the faulting lines.

3. Determine Causality:
   - Set Introduced=true ONLY IF you are absolutely certain:
     * There is clear, unambiguous, and conclusive evidence that the crash was directly introduced
       or caused by the patch series.
     * The crash occurs directly in new or modified code introduced by the patch series, or the patch series
       altered data structures, locking, object lifetimes, or preconditions in a way that directly
       triggered the failure in existing code.
   - Set Introduced=false IF:
     * There is any doubt, ambiguity, or lack of conclusive proof that the patch series caused the bug.
     * The crash occurs in an unrelated subsystem or unmodified code path whose behavior is independent
       of the patch series.
     * The crash is a pre-existing kernel issue that was randomly triggered during fuzzing.

4. Formulate Output:
   - Set Introduced to true or false.
   - In Reasoning, provide a clear, step-by-step technical explanation detailing the crash type,
     the key stack frames, whether the affected code/structures were modified by the patch series,
     and the causal justification for your verdict.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Target architecture: amd64

The kernel crash report to triage is:

INFO: task syz.2.1137:10687 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.1137      state:D stack:26176 pid:10687 tgid:10682 ppid:5596   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
  307.314502][   T37]
 __schedule+0x17db/0x58f0
 schedule+0x164/0x2b0
 schedule_preempt_disabled+0x13/0x30
 rwsem_down_write_slowpath+0x87d/0x1080
 down_write+0x1bc/0x200
 fuse_file_fallocate+0x2d8/0x8a0
 vfs_fallocate+0x65a/0x7e0
 madvise_vma_behavior+0x2fc2/0x4cb0
 madvise_walk_vmas+0x57d/0xb70
 madvise_do_behavior+0x385/0x540
 do_madvise+0x327/0x3a0
 __x64_sys_madvise+0xa6/0xc0
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f708119f559
RSP: 002b:00007f708212a028 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f7081426090 RCX: 00007f708119f559
RDX: 0000000000000009 RSI: 0000000000600002 RDI: 0000200000000000
RBP: 00007f7081236b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7081426128 R14: 00007f7081426090 R15: 00007ffcd15dd688
 </TASK>

Showing all locks held in the system:
locks held by kworker/u10:0/30: 3, on CPU#1:
 #0: ffff8881000ac140 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #1: ffffc90000a57c40 ((work_completion)(&pool->idle_cull_work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #2: ffff88823c63bd60 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2d/0x160
locks held by kworker/1:1/35: 3, on CPU#1:
 #0: ffff888106a90140 ((wq_completion)md_misc){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #1: ffffc90000aa7c40 ((work_completion)(&mddev->sync_work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #2: ffff88817861c0a0 (&mddev->suspend_mutex){+.+.}-{4:4}, at: mddev_suspend+0x139/0x6f0
locks held by khungtaskd/37: 1, last CPU#0:
 #0: ffffffff8fd5c8e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180
locks held by kworker/u9:2/56: 5, last CPU#0:
 #0: ffff8881000ac140 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #1: ffffc9000142fc40 ((work_completion)(&(&kfence_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #2: ffffffff8fbe99b0 (cpu_hotplug_lock){++++}-{0:0}, at: static_key_disable+0x12/0x20
 #3: ffffffff8fe389e0 (jump_label_mutex){+.+.}-{4:4}, at: static_key_disable_cpuslocked+0x8d/0x1a0
 #4: ffffffff8fbff760 (text_mutex){+.+.}-{4:4}, at: arch_jump_label_transform_apply+0x17/0x30
locks held by kworker/0:3/5008: 1, last CPU#0:
 #0: ffffffff8fd5c8e0 (rcu_read_lock){....}-{1:3}, at: process_scheduled_works+0x97a/0x1630
locks held by getty/5421: 2, on CPU#1:
 #0: ffff88810f0140a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70
 #1: ffffc9000348b2e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45a/0x1360
locks held by sshd/5523: 2, last CPU#0:
 #0: ffff88816fc26b08 (vm_lock){++++}-{0:0}, at: lock_vma_under_rcu+0x1d1/0x500
 #1: ffffffff8fd5c8e0 (rcu_read_lock){....}-{1:3}, at: __pte_offset_map+0x29/0x240
locks held by syz.2.1137/10683: 4, last CPU#0:
 #0: ffff8881bdcc64f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff888110b8e460 (sb_writers#16){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0
 #2: ffff88810ffeb240 (&sb->s_type->i_mutex_key#31){+.+.}-{4:4}, at: fuse_file_write_iter+0xb7f/0x11b0
 #3: ffffffff8fd5c8e0 (rcu_read_lock){....}-{1:3}, at: unwind_next_frame+0x8f/0x2550
locks held by syz.2.1137/10687: 2, on CPU#1:
 #0: ffff888110b8e460 (sb_writers#16){.+.+}-{0:0}, at: vfs_fallocate+0x5e0/0x7e0
 #1: ffff88810ffeb240 (&sb->s_type->i_mutex_key#31){+.+.}-{4:4}, at: fuse_file_fallocate+0x2d8/0x8a0
locks held by syz.4.2501/19616: 1, last CPU#1:
 #0: ffff88810d866540 (&mm->mmap_lock){++++}-{4:4}, at: __se_sys_move_pages+0x149d/0x1c80

=============================================

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 nmi_cpu_backtrace+0x274/0x2d0
 nmi_trigger_cpumask_backtrace+0x17d/0x390
 sys_info+0x135/0x170
 watchdog+0xfd7/0x1030
 kthread+0x38b/0x480
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 16 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:io_serial_out+0x7c/0xc0
Code: 6a 52 fc 44 89 f9 d3 e5 49 83 c6 40 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 7c 4b c4 fc 41 03 2e 89 d8 89 ea ee <5b> 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc 44 89 f9 80 e1 07 38 c1
RSP: 0018:ffffc90000157900 EFLAGS: 00000002
RAX: 000000000000003a RBX: 000000000000003a RCX: 0000000000000000
RDX: 00000000000003f8 RSI: 0000000000000000 RDI: 0000000000000020
RBP: 00000000000003f8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: ffffffff8575b7e0 R12: dffffc0000000000
R13: 000000000000003a R14: ffffffff9bd4fe80 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8882a7cbb000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000008000 CR3: 0000000112fa6000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 __serial8250_console_fifo_write+0x1e6/0x3e0
 serial8250_console_write+0xaa1/0x1200
 nbcon_emit_next_record+0xef5/0x1a90
 nbcon_kthread_func+0x679/0x880
 kthread+0x38b/0x480
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30
 </TASK>



Overview of modified files in the workspace:
arch/powerpc/kernel/isa-bridge.c |   5 +-
 arch/powerpc/kernel/pci_64.c     |   4 +-
 include/linux/kmsan.h            |   8 ++-
 mm/kmsan/hooks.c                 |  21 ++++---
 mm/kmsan/shadow.c                |   9 ++-
 mm/percpu-vm.c                   |   5 +-
 mm/vmalloc.c                     | 126 ++++++++++++++++++++++++++++-----------
 mm/vmalloc.h                     |   6 +-
 8 files changed, 128 insertions(+), 56 deletions(-)



The patch series contains 10 patches:
[1] [PATCH v3 01/10] mm/kmsan: undo the shadow mapping when the origin mapping fails
[2] [PATCH v3 02/10] mm/kmsan: skip vunmap_range_noflush when KMSAN is disabled
[3] [PATCH v3 03/10] mm/vmalloc: clamp an unaligned range in vunmap_pte_range()
[4] [PATCH v3 04/10] mm/vmalloc: propagate errors in vmap_pages_p*d_range()
[5] [PATCH v3 05/10] mm/vmalloc: reject an unaligned range in vmap_pages_pte_range()
[6] [PATCH v3 06/10] mm/vmalloc: reject empty and unaligned ranges in __vmap_pages_range_noflush()
[7] [PATCH v3 07/10] mm/vmalloc: only flush the cache after the vmap succeeded
[8] [PATCH v3 08/10] mm/vmalloc: undo partial mappings inside the mapping functions
[9] [PATCH v3 09/10] powerpc: drop redundant unmaps of failed vmap mappings
[10] [PATCH v3 10/10] mm/percpu: stop unmapping the CPU that failed to map

gemini-3.8-flash

null

null

							input: 6489
							output: 14
							thoughts: 921
						

**Analyzing a Hung Task Crash**

Okay, let's break this down. I've got a hung task crash report. The message screams "blocked for over 143 seconds!" and the culprit is `syz.2.1137:10687`. The call trace points us towards `fuse_file_fallocate`, which is interesting. It looks like the process is getting hung up during `rwsem_down_write_slowpath`, a standard semaphore waiting function.

Now, let's look closer at the held locks. Syz.2.1137/10683 is holding several locks: `f->f_pos_lock`, `sb_writers#16`, `&sb->s_type->i_mutex_key#31` (inode_lock), and an RCU read lock.  Meanwhile, syz.2.1137/10687 on a different CPU is waiting on `sb_writers#16` and trying to grab `&sb->s_type->i_mutex_key#31` (inode_lock) as well, in `fuse_file_fallocate`.

Aha! It's a classic deadlock situation.  Sy2.1137/10683 is already holding `inode_lock` (represented by `&sb->s_type->i_mutex_key#31`) within `fuse_file_write_iter`. Meanwhile, syz.2.1137/10687 is blocked on the *same* lock in `fuse_file_fallocate`!  This confirms it, it is a deadlock. This is why syz.2.1137/10687 is hung. And 143 seconds is a long time.

Before I go digging deeper, I want to see what the context is. What code changes are at play here? I need to review the related patch series.  I'll pull up `series-patches` or `git-show` to get the lay of the land and understand the recent modifications to this area of the code. That should give me a good starting point to hunt down the root cause.

{
  "Stat": true
}

{
  "Output": "commit bb7bf7ea43b3cb6d05755738f0163e0f990a7ef0\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Oct 26 13:05:40 2026 +0000\n\n    syz-cluster: applied patch under review\n\n arch/powerpc/kernel/isa-bridge.c |   5 +-\n arch/powerpc/kernel/pci_64.c     |   4 +-\n include/linux/kmsan.h            |   8 ++-\n mm/kmsan/hooks.c                 |  21 ++++---\n mm/kmsan/shadow.c                |   9 ++-\n mm/percpu-vm.c                   |   5 +-\n mm/vmalloc.c                     | 126 ++++++++++++++++++++++++++++-----------\n mm/vmalloc.h                     |   6 +-\n 8 files changed, 128 insertions(+), 56 deletions(-)\n"
}

gemini-3.8-flash

null

null

							input: 8158
							output: 16
							thoughts: 340
						

**Analyzing the Memory Management Patches**

Okay, let's dive into these patches. My initial impression is that they're focused on refining the kernel's memory management, specifically concerning vmalloc and KMSAN. The v3 designation suggests this is a refined version, indicating an iterative improvement process.

Patch [1] is intriguing; it seems to be addressing a potential race condition or inconsistency in KMSAN's shadow mapping. The idea to undo the shadow mapping if the original mapping fails is sound, preventing false positives or missed errors.

Patch [2] is a classic optimization, skipping `vunmap_range_noflush` when KMSAN is disabled. That’s a sensible approach to avoid unnecessary overhead when the instrumentation isn't active.

Patches [3] through [6] look like they're solidifying the vmalloc implementation by enforcing stricter alignment checks. Clamping unaligned ranges in `vunmap_pte_range()` and outright rejecting unaligned or empty ranges in `vmap_pages_p*d_range()` and `__vmap_pages_range_noflush()` is crucial for preventing unexpected behavior and potential security vulnerabilities. Propagation of errors in `vmap_pages_p*d_range()` is equally important. These are critical robustness improvements.

Patch [7] is another optimization; flushing the cache only after a successful vmap operation avoids potentially wasted cycles when a mapping fails midway through. Good defensive programming.

Patch [8] reinforces the error handling by ensuring partial mappings are undone within the mapping functions. This is a crucial defense against memory leaks or corruption on mapping failure.

Patch [9] is a PowerPC-specific optimization, removing redundant unmap operations. This suggests that the PowerPC architecture may have had some specific inefficiencies in its vmap handling.

Finally, Patch [10] tackles a per-CPU issue by preventing unmapping the CPU that failed to map. This potentially addresses a subtle race condition in a multi-CPU environment.

I'm keen to inspect the diff of HEAD to understand the overall context and how these patches fit into the existing code. Overall, these are a series of targeted improvements that should boost the stability, robustness, and performance of the memory management subsystem.

{
  "Commit": "HEAD"
}

{
  "Output": "commit bb7bf7ea43b3cb6d05755738f0163e0f990a7ef0\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Oct 26 13:05:40 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/arch/powerpc/kernel/isa-bridge.c b/arch/powerpc/kernel/isa-bridge.c\nindex 5c064485197a9..93029d85e6eaf 100644\n--- a/arch/powerpc/kernel/isa-bridge.c\n+++ b/arch/powerpc/kernel/isa-bridge.c\n@@ -46,9 +46,8 @@ static void remap_isa_base(phys_addr_t pa, unsigned long size)\n \tWARN_ON_ONCE(size \u0026 ~PAGE_MASK);\n \n \tif (slab_is_available()) {\n-\t\tif (vmap_page_range(ISA_IO_BASE, ISA_IO_BASE + size, pa,\n-\t\t\t\t    pgprot_noncached(PAGE_KERNEL)))\n-\t\t\tvunmap_range(ISA_IO_BASE, ISA_IO_BASE + size);\n+\t\tvmap_page_range(ISA_IO_BASE, ISA_IO_BASE + size, pa,\n+\t\t\t\tpgprot_noncached(PAGE_KERNEL));\n \t} else {\n \t\tearly_ioremap_range(ISA_IO_BASE, pa, size,\n \t\t\t\tpgprot_noncached(PAGE_KERNEL));\ndiff --git a/arch/powerpc/kernel/pci_64.c b/arch/powerpc/kernel/pci_64.c\nindex e27342ef128b8..f74269636d5ec 100644\n--- a/arch/powerpc/kernel/pci_64.c\n+++ b/arch/powerpc/kernel/pci_64.c\n@@ -139,10 +139,8 @@ void __iomem *ioremap_phb(phys_addr_t paddr, unsigned long size)\n \n \taddr = (unsigned long)area-\u003eaddr;\n \tif (ioremap_page_range(addr, addr + size, paddr,\n-\t\t\tpgprot_noncached(PAGE_KERNEL))) {\n-\t\tvunmap_range(addr, addr + size);\n+\t\t\tpgprot_noncached(PAGE_KERNEL)))\n \t\treturn NULL;\n-\t}\n \n \treturn (void __iomem *)addr;\n }\ndiff --git a/include/linux/kmsan.h b/include/linux/kmsan.h\nindex 7da9fd506b390..0016c032d1e79 100644\n--- a/include/linux/kmsan.h\n+++ b/include/linux/kmsan.h\n@@ -150,11 +150,14 @@ int __must_check kmsan_vmap_pages_range_noflush(unsigned long start,\n  * kmsan_vunmap_kernel_range_noflush() - Notify KMSAN about a vunmap.\n  * @start: start of vunmapped range.\n  * @end:   end of vunmapped range.\n+ * @can_resched: whether the unmap walk may call cond_resched(); pass\n+ * false from atomic context.\n  *\n  * KMSAN unmaps the contiguous metadata ranges created by\n  * kmsan_map_kernel_range_noflush().\n  */\n-void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end);\n+void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t\tbool can_resched);\n \n /**\n  * kmsan_ioremap_page_range() - Notify KMSAN about a ioremap_page_range() call.\n@@ -355,7 +358,8 @@ static inline int __must_check kmsan_vmap_pages_range_noflush(\n }\n \n static inline void kmsan_vunmap_range_noflush(unsigned long start,\n-\t\t\t\t\t      unsigned long end)\n+\t\t\t\t\t      unsigned long end,\n+\t\t\t\t\t      bool can_resched)\n {\n }\n \ndiff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c\nindex a706666db0973..0cd1edaa1120c 100644\n--- a/mm/kmsan/hooks.c\n+++ b/mm/kmsan/hooks.c\n@@ -136,10 +136,16 @@ static unsigned long vmalloc_origin(unsigned long addr)\n \t\t\t\t\t\t KMSAN_META_ORIGIN);\n }\n \n-void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end)\n+void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t\tbool can_resched)\n {\n-\t__vunmap_range_noflush(vmalloc_shadow(start), vmalloc_shadow(end));\n-\t__vunmap_range_noflush(vmalloc_origin(start), vmalloc_origin(end));\n+\tif (!kmsan_enabled)\n+\t\treturn;\n+\n+\t__vunmap_range_noflush(vmalloc_shadow(start), vmalloc_shadow(end),\n+\t\t\t       can_resched);\n+\t__vunmap_range_noflush(vmalloc_origin(start), vmalloc_origin(end),\n+\t\t\t       can_resched);\n \tflush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));\n \tflush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));\n }\n@@ -168,8 +174,9 @@ static void kmsan_iounmap_pages(unsigned long start, unsigned long end)\n \t\tif (origin)\n \t\t\t__free_pages(origin, KMSAN_IOREMAP_META_ORDER);\n \t}\n-\t__vunmap_range_noflush(shadow_start, shadow_end);\n-\t__vunmap_range_noflush(origin_start, origin_end);\n+\t/* ioremap metadata mappings are always GFP_KERNEL, so resched is safe. */\n+\t__vunmap_range_noflush(shadow_start, shadow_end, true);\n+\t__vunmap_range_noflush(origin_start, origin_end, true);\n \tflush_tlb_kernel_range(shadow_start, shadow_end);\n \tflush_tlb_kernel_range(origin_start, origin_end);\n }\n@@ -204,7 +211,7 @@ int kmsan_ioremap_page_range(unsigned long start, unsigned long end,\n \t\tmapped = __vmap_pages_range_noflush(\n \t\t\tvmalloc_shadow(start + off),\n \t\t\tvmalloc_shadow(start + off + PAGE_SIZE), prot, \u0026shadow,\n-\t\t\tPAGE_SHIFT);\n+\t\t\tPAGE_SHIFT, gfp_mask);\n \t\tif (mapped) {\n \t\t\terr = mapped;\n \t\t\tgoto ret;\n@@ -214,7 +221,7 @@ int kmsan_ioremap_page_range(unsigned long start, unsigned long end,\n \t\tmapped = __vmap_pages_range_noflush(\n \t\t\tvmalloc_origin(start + off),\n \t\t\tvmalloc_origin(start + off + PAGE_SIZE), prot, \u0026origin,\n-\t\t\tPAGE_SHIFT);\n+\t\t\tPAGE_SHIFT, gfp_mask);\n \t\tif (mapped) {\n \t\t\terr = mapped;\n \t\t\tgoto ret;\ndiff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c\nindex 0c88d89bf0d68..452760a333e4f 100644\n--- a/mm/kmsan/shadow.c\n+++ b/mm/kmsan/shadow.c\n@@ -247,7 +247,7 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,\n \torigin_end = vmalloc_meta((void *)end, KMSAN_META_ORIGIN);\n \tkmsan_enter_runtime();\n \tmapped = __vmap_pages_range_noflush(shadow_start, shadow_end, prot,\n-\t\t\t\t\t    s_pages, page_shift);\n+\t\t\t\t\t    s_pages, page_shift, gfp_mask);\n \tkmsan_leave_runtime();\n \tif (mapped) {\n \t\terr = mapped;\n@@ -255,9 +255,14 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,\n \t}\n \tkmsan_enter_runtime();\n \tmapped = __vmap_pages_range_noflush(origin_start, origin_end, prot,\n-\t\t\t\t\t    o_pages, page_shift);\n+\t\t\t\t\t    o_pages, page_shift, gfp_mask);\n \tkmsan_leave_runtime();\n \tif (mapped) {\n+\t\t/* Undo the shadow mapping set up above. */\n+\t\tkmsan_enter_runtime();\n+\t\t__vunmap_range_noflush(shadow_start, shadow_end,\n+\t\t\t\t       gfpflags_allow_blocking(gfp_mask));\n+\t\tkmsan_leave_runtime();\n \t\terr = mapped;\n \t\tgoto ret;\n \t}\ndiff --git a/mm/percpu-vm.c b/mm/percpu-vm.c\nindex 509d8901835cd..59d3a336a6bd1 100644\n--- a/mm/percpu-vm.c\n+++ b/mm/percpu-vm.c\n@@ -252,10 +252,11 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk, struct page **pages,\n \treturn 0;\n err:\n \tfor_each_possible_cpu(tcpu) {\n-\t\t__pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),\n-\t\t\t\t   page_end - page_start);\n+\t\t/* The failing CPU's partial mapping undoes itself */\n \t\tif (tcpu == cpu)\n \t\t\tbreak;\n+\t\t__pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),\n+\t\t\t\t   page_end - page_start);\n \t}\n \tpcpu_post_unmap_tlb_flush(chunk, page_start, page_end);\n \treturn err;\ndiff --git a/mm/vmalloc.c b/mm/vmalloc.c\nindex 44e0eb32708f1..2b68f7263d531 100644\n--- a/mm/vmalloc.c\n+++ b/mm/vmalloc.c\n@@ -359,11 +359,17 @@ int vmap_page_range(unsigned long addr, unsigned long end,\n \n \terr = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),\n \t\t\t\t ioremap_max_page_shift);\n-\tflush_cache_vmap(addr, end);\n \tif (!err)\n \t\terr = kmsan_ioremap_page_range(addr, end, phys_addr, prot,\n \t\t\t\t\t       ioremap_max_page_shift);\n-\treturn err;\n+\tif (err) {\n+\t\t/* Callers are ioremap and arch setup code, always sleepable. */\n+\t\t__vunmap_range_noflush(addr, end, true);\n+\t\treturn err;\n+\t}\n+\n+\tflush_cache_vmap(addr, end);\n+\treturn 0;\n }\n \n int ioremap_page_range(unsigned long addr, unsigned long end,\n@@ -393,6 +399,11 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,\n \tpte_t ptent;\n \tunsigned long size = PAGE_SIZE;\n \n+\tif (WARN_ON_ONCE(!PAGE_ALIGNED(end - addr)))\n+\t\tend = addr + PAGE_ALIGN_DOWN(end - addr);\n+\tif (end == addr)\n+\t\treturn;\n+\n \tpte = pte_offset_kernel(pmd, addr);\n \tlazy_mmu_mode_enable();\n \n@@ -418,7 +429,7 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,\n }\n \n static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,\n-\t\t\t     pgtbl_mod_mask *mask)\n+\t\t\t     pgtbl_mod_mask *mask, bool can_resched)\n {\n \tpmd_t *pmd;\n \tunsigned long next;\n@@ -440,12 +451,14 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,\n \t\t\tcontinue;\n \t\tvunmap_pte_range(pmd, addr, next, mask);\n \n-\t\tcond_resched();\n+\t\t/* The undo path may run in atomic context. */\n+\t\tif (can_resched)\n+\t\t\tcond_resched();\n \t} while (pmd++, addr = next, addr != end);\n }\n \n static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,\n-\t\t\t     pgtbl_mod_mask *mask)\n+\t\t\t     pgtbl_mod_mask *mask, bool can_resched)\n {\n \tpud_t *pud;\n \tunsigned long next;\n@@ -465,12 +478,12 @@ static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,\n \t\t}\n \t\tif (pud_none_or_clear_bad(pud))\n \t\t\tcontinue;\n-\t\tvunmap_pmd_range(pud, addr, next, mask);\n+\t\tvunmap_pmd_range(pud, addr, next, mask, can_resched);\n \t} while (pud++, addr = next, addr != end);\n }\n \n static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n-\t\t\t     pgtbl_mod_mask *mask)\n+\t\t\t     pgtbl_mod_mask *mask, bool can_resched)\n {\n \tp4d_t *p4d;\n \tunsigned long next;\n@@ -485,7 +498,7 @@ static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n \n \t\tif (p4d_none_or_clear_bad(p4d))\n \t\t\tcontinue;\n-\t\tvunmap_pud_range(p4d, addr, next, mask);\n+\t\tvunmap_pud_range(p4d, addr, next, mask, can_resched);\n \t} while (p4d++, addr = next, addr != end);\n }\n \n@@ -501,7 +514,8 @@ static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n  *\n  * This is an internal function only. Do not use outside mm/.\n  */\n-void __vunmap_range_noflush(unsigned long start, unsigned long end)\n+void __vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t    bool can_resched)\n {\n \tunsigned long next;\n \tpgd_t *pgd;\n@@ -516,7 +530,7 @@ void __vunmap_range_noflush(unsigned long start, unsigned long end)\n \t\t\tmask |= PGTBL_PGD_MODIFIED;\n \t\tif (pgd_none_or_clear_bad(pgd))\n \t\t\tcontinue;\n-\t\tvunmap_p4d_range(pgd, addr, next, \u0026mask);\n+\t\tvunmap_p4d_range(pgd, addr, next, \u0026mask, can_resched);\n \t} while (pgd++, addr = next, addr != end);\n \n \tif (mask \u0026 ARCH_PAGE_TABLE_SYNC_MASK)\n@@ -525,8 +539,9 @@ void __vunmap_range_noflush(unsigned long start, unsigned long end)\n \n void vunmap_range_noflush(unsigned long start, unsigned long end)\n {\n-\tkmsan_vunmap_range_noflush(start, end);\n-\t__vunmap_range_noflush(start, end);\n+\t/* The unmap paths are sleepable, keep the resched point. */\n+\tkmsan_vunmap_range_noflush(start, end, true);\n+\t__vunmap_range_noflush(start, end, true);\n }\n \n /**\n@@ -552,6 +567,9 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,\n \tint err = 0;\n \tpte_t *pte;\n \n+\tif (WARN_ON_ONCE(!PAGE_ALIGNED(end - addr)))\n+\t\treturn -EINVAL;\n+\n \t/*\n \t * nr is a running index into the array which helps higher level\n \t * callers keep track of where we're up to.\n@@ -595,16 +613,18 @@ static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr,\n {\n \tpmd_t *pmd;\n \tunsigned long next;\n+\tint err = 0;\n \n \tpmd = pmd_alloc_track(\u0026init_mm, pud, addr, mask);\n \tif (!pmd)\n \t\treturn -ENOMEM;\n \tdo {\n \t\tnext = pmd_addr_end(addr, end);\n-\t\tif (vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask))\n-\t\t\treturn -ENOMEM;\n+\t\terr = vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask);\n+\t\tif (err)\n+\t\t\tbreak;\n \t} while (pmd++, addr = next, addr != end);\n-\treturn 0;\n+\treturn err;\n }\n \n static int vmap_pages_pud_range(p4d_t *p4d, unsigned long addr,\n@@ -613,16 +633,18 @@ static int vmap_pages_pud_range(p4d_t *p4d, unsigned long addr,\n {\n \tpud_t *pud;\n \tunsigned long next;\n+\tint err = 0;\n \n \tpud = pud_alloc_track(\u0026init_mm, p4d, addr, mask);\n \tif (!pud)\n \t\treturn -ENOMEM;\n \tdo {\n \t\tnext = pud_addr_end(addr, end);\n-\t\tif (vmap_pages_pmd_range(pud, addr, next, prot, pages, nr, mask))\n-\t\t\treturn -ENOMEM;\n+\t\terr = vmap_pages_pmd_range(pud, addr, next, prot, pages, nr, mask);\n+\t\tif (err)\n+\t\t\tbreak;\n \t} while (pud++, addr = next, addr != end);\n-\treturn 0;\n+\treturn err;\n }\n \n static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr,\n@@ -631,16 +653,18 @@ static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr,\n {\n \tp4d_t *p4d;\n \tunsigned long next;\n+\tint err = 0;\n \n \tp4d = p4d_alloc_track(\u0026init_mm, pgd, addr, mask);\n \tif (!p4d)\n \t\treturn -ENOMEM;\n \tdo {\n \t\tnext = p4d_addr_end(addr, end);\n-\t\tif (vmap_pages_pud_range(p4d, addr, next, prot, pages, nr, mask))\n-\t\t\treturn -ENOMEM;\n+\t\terr = vmap_pages_pud_range(p4d, addr, next, prot, pages, nr, mask);\n+\t\tif (err)\n+\t\t\tbreak;\n \t} while (p4d++, addr = next, addr != end);\n-\treturn 0;\n+\treturn err;\n }\n \n static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,\n@@ -677,33 +701,51 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,\n  * The caller is responsible for calling flush_cache_vmap() after this\n  * function returns successfully and before the addresses are accessed.\n  *\n+ * On failure the mapping is torn down before returning, so a retry\n+ * sees a clean range. When @gfp_mask cannot block, the teardown\n+ * skips cond_resched(), it may run in atomic context.\n+ *\n  * This is an internal function only. Do not use outside mm/.\n  */\n int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n-\t\tpgprot_t prot, struct page **pages, unsigned int page_shift)\n+\t\tpgprot_t prot, struct page **pages, unsigned int page_shift,\n+\t\tgfp_t gfp_mask)\n {\n \tunsigned int i, nr = (end - addr) \u003e\u003e PAGE_SHIFT;\n+\tunsigned long start = addr;\n+\tint err = 0;\n \n-\tif (WARN_ON_ONCE(page_shift \u003c PAGE_SHIFT))\n+\tif (WARN_ON_ONCE(addr \u003e= end))\n \t\treturn -EINVAL;\n \n-\tif (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||\n-\t\t\tpage_shift == PAGE_SHIFT)\n-\t\treturn vmap_small_pages_range_noflush(addr, end, prot, pages);\n+\tif (WARN_ON_ONCE(!PAGE_ALIGNED(addr) || !PAGE_ALIGNED(end)))\n+\t\treturn -EINVAL;\n \n-\tfor (i = 0; i \u003c nr; i += 1U \u003c\u003c (page_shift - PAGE_SHIFT)) {\n-\t\tint err;\n+\tif (WARN_ON_ONCE(page_shift \u003c PAGE_SHIFT))\n+\t\treturn -EINVAL;\n \n-\t\terr = vmap_range_noflush(addr, addr + (1UL \u003c\u003c page_shift),\n+\tif (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||\n+\t\t\tpage_shift == PAGE_SHIFT) {\n+\t\terr = vmap_small_pages_range_noflush(addr, end, prot, pages);\n+\t} else {\n+\t\tfor (i = 0; i \u003c nr; i += 1U \u003c\u003c (page_shift - PAGE_SHIFT)) {\n+\t\t\terr = vmap_range_noflush(addr,\n+\t\t\t\t\taddr + (1UL \u003c\u003c page_shift),\n \t\t\t\t\tpage_to_phys(pages[i]), prot,\n \t\t\t\t\tpage_shift);\n-\t\tif (err)\n-\t\t\treturn err;\n+\t\t\tif (err)\n+\t\t\t\tbreak;\n \n-\t\taddr += 1UL \u003c\u003c page_shift;\n+\t\t\taddr += 1UL \u003c\u003c page_shift;\n+\t\t}\n \t}\n \n-\treturn 0;\n+\t/* Undo the PTEs installed before the failure. */\n+\tif (err)\n+\t\t__vunmap_range_noflush(start, end,\n+\t\t\t\t       gfpflags_allow_blocking(gfp_mask));\n+\n+\treturn err;\n }\n \n int vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n@@ -715,7 +757,18 @@ int vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n \n \tif (ret)\n \t\treturn ret;\n-\treturn __vmap_pages_range_noflush(addr, end, prot, pages, page_shift);\n+\n+\tret = __vmap_pages_range_noflush(addr, end, prot, pages, page_shift,\n+\t\t\t\t\t gfp_mask);\n+\t/*\n+\t * The page tables undo themselves on failure. Tear down the\n+\t * metadata that was fully set up before the mapping failed.\n+\t */\n+\tif (ret)\n+\t\tkmsan_vunmap_range_noflush(addr, end,\n+\t\t\t\t\t   gfpflags_allow_blocking(gfp_mask));\n+\n+\treturn ret;\n }\n \n static int __vmap_pages_range(unsigned long addr, unsigned long end,\n@@ -725,8 +778,11 @@ static int __vmap_pages_range(unsigned long addr, unsigned long end,\n \tint err;\n \n \terr = vmap_pages_range_noflush(addr, end, prot, pages, page_shift, gfp_mask);\n+\tif (err)\n+\t\treturn err;\n+\n \tflush_cache_vmap(addr, end);\n-\treturn err;\n+\treturn 0;\n }\n \n /**\ndiff --git a/mm/vmalloc.h b/mm/vmalloc.h\nindex d8372a4f65c4c..9ea28845f7133 100644\n--- a/mm/vmalloc.h\n+++ b/mm/vmalloc.h\n@@ -40,10 +40,12 @@ void clear_vm_uninitialized_flag(struct vm_struct *vm);\n \n int __must_check __vmap_pages_range_noflush(unsigned long addr,\n \t\tunsigned long end, pgprot_t prot,\n-\t\tstruct page **pages, unsigned int page_shift);\n+\t\tstruct page **pages, unsigned int page_shift,\n+\t\tgfp_t gfp_mask);\n \n void vunmap_range_noflush(unsigned long start, unsigned long end);\n \n-void __vunmap_range_noflush(unsigned long start, unsigned long end);\n+void __vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t    bool can_resched);\n \n #endif /* __MM_VMALLOC_H */\n"
}

gemini-3.8-flash

null

null

							input: 15630
							output: 28
							thoughts: 1581
						

**Crash Report Analysis and Hypothesis Formation**

Alright, let's dive into this crash report. The initial message indicates a task, `syz.2.1137:10687`, has been blocked for an extended period, which is never a good sign. The call trace points us toward the root cause, so let's parse that. It seems the task is stuck in a `down_write` operation within `fuse_file_fallocate`, which is called from `vfs_fallocate`, ultimately stemming from a `madvise_vma_behavior` call. Immediately, I think "rwsem," and know that points me towards a potential locking issue.

The report also shows that task 10687 is blocked waiting for inode lock `&sb->s_type->i_mutex_key#31`. This seems interesting. Looking into the locks held by other tasks, specifically task 10683, reveals this task has locked the same inode, the same mutex. And, its call stack shows it performing a `fuse_file_write_iter` operation. 

Knowing this, I immediately suspect a FUSE-related deadlock or hang. Because the function calls are going to `fuse_file_write_iter` and `fuse_file_fallocate`, which are waiting on a response from a userspace FUSE daemon, the daemon could be stalled, or dead. This can definitely cause indefinite hangs.

Now, my mind shifts to: did a recent patch series introduce this behavior? The report gives me some files that were modified: `arch/powerpc/kernel/isa-bridge.c`, `arch/powerpc/kernel/pci_64.c`, `include/linux/kmsan.h`, `mm/kmsan/hooks.c`, `mm/kmsan/shadow.c`, `mm/percpu-vm.c`, `mm/vmalloc.c`, and `mm/vmalloc.h`. None of these *directly* seem relevant to FUSE, or any part of the call trace from the crash report ( `rwsem`, `vfs`, `madvise`, `vmalloc`). 

However, since `madvise_vma_behavior` ultimately leads to a `vfs_fallocate` call, which is then calling `fuse_file_fallocate`, I need to consider what `madvise_vma_behavior` does. Specifically, I recall that `MADV_REMOVE` uses `vfs_fallocate` with `FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE`. Is there anything the patch series touched, that may cause `MADV_REMOVE` to interact poorly with FUSE?

I will need to check the source code for `madvise_vma_behavior` to confirm this hypothesis, but given the information, that seems to be the place to start.

{
  "Expression": "vfs_fallocate",
  "PathPrefixes": [
    "mm/"
  ]
}

{
  "Output": "mm/madvise.c=1012=static long madvise_remove(struct madvise_behavior *madv_behavior)\n--\nmm/madvise.c-1049-\t}\nmm/madvise.c:1050:\terror = vfs_fallocate(f,\nmm/madvise.c-1051-\t\t\t\tFALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,\n"
}

gemini-3.8-flash

null

null

							input: 17986
							output: 36
							thoughts: 21
						

Here's my take on those thoughts, tailored for an expert audience:

**Diving into `madvise_remove`**

Okay, so I need to understand the specifics of how `madvise_remove` functions. I'll head straight into `mm/madvise.c` – that's where the core logic will be. I want to see precisely how it handles the unmapping of pages, what memory management structures it touches, and, critically, how it integrates with the overall VM system. I'm looking for the nitty-gritty details on page table invalidation, potential coalescing of adjacent regions, and, of course, the implications for dirty pages and swap space. I'll be particularly interested in the interaction between `madvise_remove` and the page cache. Does it actively clean up cache entries? Does it bypass any established caching strategies? And what are the locking implications – how is concurrency handled when a process is calling `madvise_remove` while other processes are accessing the same memory region? This goes way beyond simple unmap operations and likely involves some complex interactions.

{
  "File": "mm/madvise.c",
  "FirstLine": 1040,
  "LineCount": 25
}

{
  "Contents": "1040:\t\t * Filesystem's fallocate may need to take i_rwsem.  We need to\n1041:\t\t * explicitly grab a reference because the vma (and hence the\n1042:\t\t * vma's reference to the file) can go away as soon as we drop\n1043:\t\t * mmap_lock.\n1044:\t\t */\n1045:\t\tget_file(f);\n1046:\t\tif (userfaultfd_remove(vma, start, end)) {\n1047:\t\t\t/* mmap_lock was not released by userfaultfd_remove() */\n1048:\t\t\tmmap_read_unlock(mm);\n1049:\t\t}\n1050:\t\terror = vfs_fallocate(f,\n1051:\t\t\t\t\tFALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,\n1052:\t\t\t\t\toffset, end - start);\n1053:\t\tfput(f);\n1054:\t\tmmap_read_lock(mm);\n1055:\t\treturn error;\n1056:\t}\n1057:\t\n1058:\tstatic bool is_valid_guard_vma(const struct vm_area_struct *vma,\n1059:\t\t\t\t       bool allow_locked)\n1060:\t{\n1061:\t\t/*\n1062:\t\t * A user could lock after setting a guard range but that's fine as\n1063:\t\t * they'd not be able to fault in. The issue arises when we try to zap\n1064:\t\t * existing locked VMAs. We don't want to do that.\n"
}

gemini-3.8-flash

null

null

							input: 18706
							output: 10
							thoughts: 887
						

**Analyzing a FUSE Deadlock with madvise_remove**

Okay, let's break this down. I'm looking at a situation where `madvise(..., MADV_REMOVE)` is causing a hang, and it's looking like a classic FUSE deadlock. The core issue seems to be a contention on the `inode_lock`. Here's what I'm seeing:

`madvise_remove` is dropping the `mmap_lock` and then calling `vfs_fallocate`. `vfs_fallocate`, as expected, goes to `fuse_file_fallocate`. Now, `fuse_file_fallocate` tries to acquire the `inode_lock`, which is actually a `down_write(&inode->i_rwsem)`.

Meanwhile, there's another task, task 10683, that's already in the FUSE file system code path. It's executing `vfs_write` and then `fuse_file_write_iter`. Within `fuse_file_write_iter`, it also acquires the `inode_lock` (represented here as `&sb->s_type->i_mutex_key#31`). Importantly, it's *holding* that lock while it's likely waiting for a response from the FUSE daemon (or perhaps the FUSE daemon is having its own problems).

So, the deadlock is clear: Task 10687, the `madvise_remove` call, is stuck, blocked on acquiring the `inode_lock`, which is currently held by task 10683. And task 10683 is likely waiting for a response from the FUSE daemon while *also* holding that lock, leading to a hang. This is a very common FUSE problem – often caused by a FUSE fuzzer, or the daemon being unresponsive.

Now, a critical next step is to see if this is related to the recent KMSAN patch series.

I'll check the patch series and see what the changes are to the memory management of the KMSAN system, and how that could possibly relate to this. The patches are:

1.  mm/kmsan: undo the shadow mapping when the origin mapping fails
2.  mm/kmsan: skip vunmap_range_noflush when KMSAN is disabled
3.  mm/vmalloc: clamp an unaligned range in vunmap_pte_range()
4.  mm/vmalloc: propagate errors in vmap_pages_p*d_range()
5.  mm/vmalloc: reject an unaligned range in vmap_pages_pte_range()
6.  mm/vmalloc: reject empty and unaligned ranges in __vmap_pages_range_noflush()
7.  mm/vmalloc: only flush the cache after the vmap succeeded
8.  mm/vmalloc: undo partial mappings inside the mapping functions
9.  powerpc: drop redundant unmaps of failed vmap mappings
10. mm/percpu: stop unmapping the CPU that failed to map

I'll have to delve into the details of these patches to see if they introduce any new locking scenarios, potentially impact how FUSE interacts with the VFS layer, or how `madvise` and `fallocate` are handled. I need to understand if these changes could have altered the timing or error handling in a way that triggers this deadlock in a new or different context.

missing argument "PatchNum"

null

{
  "error": "missing argument \"PatchNum\""
}

gemini-3.8-flash

null

null

							input: 20367
							output: 15
							thoughts: 17
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Initiating the Patch Series**

Right, let's kick this off. My immediate instinct is to call `series-patches`. No surprises there, that's where we start when working with a patch series. And naturally, the first patch, the base of the series, is going to have a `PatchNum` of `0`. No need to overthink it at this stage; this is the logical and expected starting point. Now the real work begins...

{
  "PatchNum": 0
}

{
  "Output": "The patch series contains 10 patches:\n[1] [PATCH v3 01/10] mm/kmsan: undo the shadow mapping when the origin mapping fails\n[2] [PATCH v3 02/10] mm/kmsan: skip vunmap_range_noflush when KMSAN is disabled\n[3] [PATCH v3 03/10] mm/vmalloc: clamp an unaligned range in vunmap_pte_range()\n[4] [PATCH v3 04/10] mm/vmalloc: propagate errors in vmap_pages_p*d_range()\n[5] [PATCH v3 05/10] mm/vmalloc: reject an unaligned range in vmap_pages_pte_range()\n[6] [PATCH v3 06/10] mm/vmalloc: reject empty and unaligned ranges in __vmap_pages_range_noflush()\n[7] [PATCH v3 07/10] mm/vmalloc: only flush the cache after the vmap succeeded\n[8] [PATCH v3 08/10] mm/vmalloc: undo partial mappings inside the mapping functions\n[9] [PATCH v3 09/10] powerpc: drop redundant unmaps of failed vmap mappings\n[10] [PATCH v3 10/10] mm/percpu: stop unmapping the CPU that failed to map\n\n(Note: PatchNum 0 was not found, showing full patch list above)"
}

gemini-3.8-flash

null

null

							input: 20869
							output: 15
							thoughts: 11
						

Okay, let's dive into this. Here's how I'd approach that prompt, keeping in mind I'm dealing with an expert audience:

**Prioritizing Patch Analysis**

Alright, my immediate focus is on "Patch 1 and 8." That's a directive I need to act upon. My initial assessment immediately zooms in on those specific patches. The request to check implies there might be a known issue or a suspected anomaly tied to those releases. My mind immediately begins running through the typical reasons I'd prioritize patches: security vulnerabilities, critical bug fixes, performance regressions, or perhaps, architectural changes. Without further context, I'll need to rapidly evaluate these patches to determine why they're flagged, and what's most important in looking into them. My process from here is likely to diverge based on how my investigation is steered.

{
  "PatchNum": 1
}

{
  "Output": "Patch [1] [PATCH v3 01/10] mm/kmsan: undo the shadow mapping when the origin mapping fails:\n\nkmsan_vmap_pages_range_noflush() first maps the shadow pages and then\nthe origin pages. If the second mapping fails, the first one is left\nmapped, and the callers do not roll it back. The next vmap of the\nsame metadata range hits the stale PTEs again and BUG()s on the huge\nmapping path, or gets -EBUSY with a WARN_ON() on the small page one.\n\nUndo the shadow mapping on that error path, the same way\nkmsan_ioremap_page_range() cleans up after a partial failure.\n__vunmap_range_noflush() only clears the PTEs; nothing has touched\nthe shadow mapping, so no TLB flush is needed.\n\nFixes: 47ebd0310e89 (\"mm: kmsan: handle alloc failures in kmsan_vmap_pages_range_noflush()\")\nCc: stable@vger.kernel.org\nReviewed-by: Suren Baghdasaryan \u003csurenb@google.com\u003e\nReviewed-by: Dev Jain \u003cdev.jain@arm.com\u003e\nSigned-off-by: Hao Ge \u003chao.ge@linux.dev\u003e\n---\n mm/kmsan/shadow.c | 4 ++++\n 1 file changed, 4 insertions(+)\n\ndiff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c\nindex 0c88d89bf0d6..2166086d3dc3 100644\n--- a/mm/kmsan/shadow.c\n+++ b/mm/kmsan/shadow.c\n@@ -258,6 +258,10 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,\n \t\t\t\t\t    o_pages, page_shift);\n \tkmsan_leave_runtime();\n \tif (mapped) {\n+\t\t/* Undo the shadow mapping set up above. */\n+\t\tkmsan_enter_runtime();\n+\t\t__vunmap_range_noflush(shadow_start, shadow_end);\n+\t\tkmsan_leave_runtime();\n \t\terr = mapped;\n \t\tgoto ret;\n \t}\n-- \n2.25.1"
}

gemini-3.8-flash

null

null

							input: 21633
							output: 15
							thoughts: 8
						

Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written in the first person:

**Diving into Patch 8**

Alright, time to get to it. Let's see what we're dealing with in Patch 8. This isn't just a casual glance; I need to understand the implications of any changes, even seemingly minor ones, on the overall system stability, performance, and most importantly, the user experience. My focus is on potential regressions. What are the known issues, and has this patch introduced anything new? I'm particularly interested in areas of the codebase that are frequently touched, complex algorithms, and performance-critical functions. I'll need to scrutinize the changelog and diffs for hints of unexpected behavior, memory leaks, or concurrency problems. Then I will need to think, at a system level, of the impacts on downstream processes or integrations. Let's dig in.

{
  "PatchNum": 8
}

{
  "Output": "Patch [8] [PATCH v3 08/10] mm/vmalloc: undo partial mappings inside the mapping functions:\n\nThe vmap entry points can install some PTEs, then fail and leave the\npartial mapping behind.\n\nThe callers do not agree on who cleans it up. pcpu_map_pages() and\nkmsan_ioremap_page_range() roll back what they mapped, while\nvm_module_tags_populate() and the __GFP_NOFAIL retry loop in\n__vmalloc_area_node() expect a clean range from the mapping function.\nFor them the leftovers stay mapped, and the next attempt to map the\nsame range fails, with a BUG() in vmap_pte_range() for huge mappings\nand a warning on the small-page path.\n\nAfter discussing with Suren and Ulad, we decided to put the rollback\ninto the entry points of the vmap API rather than into every low-level\nhelper. __vmap_pages_range_noflush() undoes the whole range it was\nasked to map when it fails, and vmap_page_range() undoes its range\nfor the ioremap-style mappings.\n\nThe rollback is __vunmap_range_noflush(), which only clears the PTEs.\nNo TLB flush is needed, nothing has touched the mapping yet.\nvmap_pages_range_noflush() also drops the KMSAN metadata of the failed\nmapping.\n\nThe undo walk skips its cond_resched() when the caller's gfp mask\ncannot block: __vmalloc() with GFP_ATOMIC or GFP_NOWAIT can run in\natomic context, where cond_resched() cannot schedule and its\n__might_resched() annotation fires on CONFIG_DEBUG_ATOMIC_SLEEP\nbuilds. __vunmap_range_noflush() takes a can_resched argument for\nthat, which the sleepable callers pass as true.\n\nReported-by: Sashiko \u003csashiko-bot@kernel.org\u003e\nSuggested-by: Uladyslau Rezki \u003curezki@gmail.com\u003e\nSigned-off-by: Hao Ge \u003chao.ge@linux.dev\u003e\n---\n include/linux/kmsan.h |  8 +++--\n mm/kmsan/hooks.c      | 18 ++++++----\n mm/kmsan/shadow.c     |  7 ++--\n mm/vmalloc.c          | 78 ++++++++++++++++++++++++++++++-------------\n mm/vmalloc.h          |  6 ++--\n 5 files changed, 79 insertions(+), 38 deletions(-)\n\ndiff --git a/include/linux/kmsan.h b/include/linux/kmsan.h\nindex 7da9fd506b39..0016c032d1e7 100644\n--- a/include/linux/kmsan.h\n+++ b/include/linux/kmsan.h\n@@ -150,11 +150,14 @@ int __must_check kmsan_vmap_pages_range_noflush(unsigned long start,\n  * kmsan_vunmap_kernel_range_noflush() - Notify KMSAN about a vunmap.\n  * @start: start of vunmapped range.\n  * @end:   end of vunmapped range.\n+ * @can_resched: whether the unmap walk may call cond_resched(); pass\n+ * false from atomic context.\n  *\n  * KMSAN unmaps the contiguous metadata ranges created by\n  * kmsan_map_kernel_range_noflush().\n  */\n-void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end);\n+void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t\tbool can_resched);\n \n /**\n  * kmsan_ioremap_page_range() - Notify KMSAN about a ioremap_page_range() call.\n@@ -355,7 +358,8 @@ static inline int __must_check kmsan_vmap_pages_range_noflush(\n }\n \n static inline void kmsan_vunmap_range_noflush(unsigned long start,\n-\t\t\t\t\t      unsigned long end)\n+\t\t\t\t\t      unsigned long end,\n+\t\t\t\t\t      bool can_resched)\n {\n }\n \ndiff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c\nindex 107f66841274..0cd1edaa1120 100644\n--- a/mm/kmsan/hooks.c\n+++ b/mm/kmsan/hooks.c\n@@ -136,13 +136,16 @@ static unsigned long vmalloc_origin(unsigned long addr)\n \t\t\t\t\t\t KMSAN_META_ORIGIN);\n }\n \n-void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end)\n+void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t\tbool can_resched)\n {\n \tif (!kmsan_enabled)\n \t\treturn;\n \n-\t__vunmap_range_noflush(vmalloc_shadow(start), vmalloc_shadow(end));\n-\t__vunmap_range_noflush(vmalloc_origin(start), vmalloc_origin(end));\n+\t__vunmap_range_noflush(vmalloc_shadow(start), vmalloc_shadow(end),\n+\t\t\t       can_resched);\n+\t__vunmap_range_noflush(vmalloc_origin(start), vmalloc_origin(end),\n+\t\t\t       can_resched);\n \tflush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));\n \tflush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));\n }\n@@ -171,8 +174,9 @@ static void kmsan_iounmap_pages(unsigned long start, unsigned long end)\n \t\tif (origin)\n \t\t\t__free_pages(origin, KMSAN_IOREMAP_META_ORDER);\n \t}\n-\t__vunmap_range_noflush(shadow_start, shadow_end);\n-\t__vunmap_range_noflush(origin_start, origin_end);\n+\t/* ioremap metadata mappings are always GFP_KERNEL, so resched is safe. */\n+\t__vunmap_range_noflush(shadow_start, shadow_end, true);\n+\t__vunmap_range_noflush(origin_start, origin_end, true);\n \tflush_tlb_kernel_range(shadow_start, shadow_end);\n \tflush_tlb_kernel_range(origin_start, origin_end);\n }\n@@ -207,7 +211,7 @@ int kmsan_ioremap_page_range(unsigned long start, unsigned long end,\n \t\tmapped = __vmap_pages_range_noflush(\n \t\t\tvmalloc_shadow(start + off),\n \t\t\tvmalloc_shadow(start + off + PAGE_SIZE), prot, \u0026shadow,\n-\t\t\tPAGE_SHIFT);\n+\t\t\tPAGE_SHIFT, gfp_mask);\n \t\tif (mapped) {\n \t\t\terr = mapped;\n \t\t\tgoto ret;\n@@ -217,7 +221,7 @@ int kmsan_ioremap_page_range(unsigned long start, unsigned long end,\n \t\tmapped = __vmap_pages_range_noflush(\n \t\t\tvmalloc_origin(start + off),\n \t\t\tvmalloc_origin(start + off + PAGE_SIZE), prot, \u0026origin,\n-\t\t\tPAGE_SHIFT);\n+\t\t\tPAGE_SHIFT, gfp_mask);\n \t\tif (mapped) {\n \t\t\terr = mapped;\n \t\t\tgoto ret;\ndiff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c\nindex 2166086d3dc3..452760a333e4 100644\n--- a/mm/kmsan/shadow.c\n+++ b/mm/kmsan/shadow.c\n@@ -247,7 +247,7 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,\n \torigin_end = vmalloc_meta((void *)end, KMSAN_META_ORIGIN);\n \tkmsan_enter_runtime();\n \tmapped = __vmap_pages_range_noflush(shadow_start, shadow_end, prot,\n-\t\t\t\t\t    s_pages, page_shift);\n+\t\t\t\t\t    s_pages, page_shift, gfp_mask);\n \tkmsan_leave_runtime();\n \tif (mapped) {\n \t\terr = mapped;\n@@ -255,12 +255,13 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,\n \t}\n \tkmsan_enter_runtime();\n \tmapped = __vmap_pages_range_noflush(origin_start, origin_end, prot,\n-\t\t\t\t\t    o_pages, page_shift);\n+\t\t\t\t\t    o_pages, page_shift, gfp_mask);\n \tkmsan_leave_runtime();\n \tif (mapped) {\n \t\t/* Undo the shadow mapping set up above. */\n \t\tkmsan_enter_runtime();\n-\t\t__vunmap_range_noflush(shadow_start, shadow_end);\n+\t\t__vunmap_range_noflush(shadow_start, shadow_end,\n+\t\t\t\t       gfpflags_allow_blocking(gfp_mask));\n \t\tkmsan_leave_runtime();\n \t\terr = mapped;\n \t\tgoto ret;\ndiff --git a/mm/vmalloc.c b/mm/vmalloc.c\nindex 96e15d6cfc6d..2b68f7263d53 100644\n--- a/mm/vmalloc.c\n+++ b/mm/vmalloc.c\n@@ -362,8 +362,11 @@ int vmap_page_range(unsigned long addr, unsigned long end,\n \tif (!err)\n \t\terr = kmsan_ioremap_page_range(addr, end, phys_addr, prot,\n \t\t\t\t\t       ioremap_max_page_shift);\n-\tif (err)\n+\tif (err) {\n+\t\t/* Callers are ioremap and arch setup code, always sleepable. */\n+\t\t__vunmap_range_noflush(addr, end, true);\n \t\treturn err;\n+\t}\n \n \tflush_cache_vmap(addr, end);\n \treturn 0;\n@@ -426,7 +429,7 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,\n }\n \n static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,\n-\t\t\t     pgtbl_mod_mask *mask)\n+\t\t\t     pgtbl_mod_mask *mask, bool can_resched)\n {\n \tpmd_t *pmd;\n \tunsigned long next;\n@@ -448,12 +451,14 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,\n \t\t\tcontinue;\n \t\tvunmap_pte_range(pmd, addr, next, mask);\n \n-\t\tcond_resched();\n+\t\t/* The undo path may run in atomic context. */\n+\t\tif (can_resched)\n+\t\t\tcond_resched();\n \t} while (pmd++, addr = next, addr != end);\n }\n \n static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,\n-\t\t\t     pgtbl_mod_mask *mask)\n+\t\t\t     pgtbl_mod_mask *mask, bool can_resched)\n {\n \tpud_t *pud;\n \tunsigned long next;\n@@ -473,12 +478,12 @@ static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,\n \t\t}\n \t\tif (pud_none_or_clear_bad(pud))\n \t\t\tcontinue;\n-\t\tvunmap_pmd_range(pud, addr, next, mask);\n+\t\tvunmap_pmd_range(pud, addr, next, mask, can_resched);\n \t} while (pud++, addr = next, addr != end);\n }\n \n static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n-\t\t\t     pgtbl_mod_mask *mask)\n+\t\t\t     pgtbl_mod_mask *mask, bool can_resched)\n {\n \tp4d_t *p4d;\n \tunsigned long next;\n@@ -493,7 +498,7 @@ static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n \n \t\tif (p4d_none_or_clear_bad(p4d))\n \t\t\tcontinue;\n-\t\tvunmap_pud_range(p4d, addr, next, mask);\n+\t\tvunmap_pud_range(p4d, addr, next, mask, can_resched);\n \t} while (p4d++, addr = next, addr != end);\n }\n \n@@ -509,7 +514,8 @@ static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n  *\n  * This is an internal function only. Do not use outside mm/.\n  */\n-void __vunmap_range_noflush(unsigned long start, unsigned long end)\n+void __vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t    bool can_resched)\n {\n \tunsigned long next;\n \tpgd_t *pgd;\n@@ -524,7 +530,7 @@ void __vunmap_range_noflush(unsigned long start, unsigned long end)\n \t\t\tmask |= PGTBL_PGD_MODIFIED;\n \t\tif (pgd_none_or_clear_bad(pgd))\n \t\t\tcontinue;\n-\t\tvunmap_p4d_range(pgd, addr, next, \u0026mask);\n+\t\tvunmap_p4d_range(pgd, addr, next, \u0026mask, can_resched);\n \t} while (pgd++, addr = next, addr != end);\n \n \tif (mask \u0026 ARCH_PAGE_TABLE_SYNC_MASK)\n@@ -533,8 +539,9 @@ void __vunmap_range_noflush(unsigned long start, unsigned long end)\n \n void vunmap_range_noflush(unsigned long start, unsigned long end)\n {\n-\tkmsan_vunmap_range_noflush(start, end);\n-\t__vunmap_range_noflush(start, end);\n+\t/* The unmap paths are sleepable, keep the resched point. */\n+\tkmsan_vunmap_range_noflush(start, end, true);\n+\t__vunmap_range_noflush(start, end, true);\n }\n \n /**\n@@ -694,12 +701,19 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,\n  * The caller is responsible for calling flush_cache_vmap() after this\n  * function returns successfully and before the addresses are accessed.\n  *\n+ * On failure the mapping is torn down before returning, so a retry\n+ * sees a clean range. When @gfp_mask cannot block, the teardown\n+ * skips cond_resched(), it may run in atomic context.\n+ *\n  * This is an internal function only. Do not use outside mm/.\n  */\n int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n-\t\tpgprot_t prot, struct page **pages, unsigned int page_shift)\n+\t\tpgprot_t prot, struct page **pages, unsigned int page_shift,\n+\t\tgfp_t gfp_mask)\n {\n \tunsigned int i, nr = (end - addr) \u003e\u003e PAGE_SHIFT;\n+\tunsigned long start = addr;\n+\tint err = 0;\n \n \tif (WARN_ON_ONCE(addr \u003e= end))\n \t\treturn -EINVAL;\n@@ -711,22 +725,27 @@ int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n \t\treturn -EINVAL;\n \n \tif (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||\n-\t\t\tpage_shift == PAGE_SHIFT)\n-\t\treturn vmap_small_pages_range_noflush(addr, end, prot, pages);\n-\n-\tfor (i = 0; i \u003c nr; i += 1U \u003c\u003c (page_shift - PAGE_SHIFT)) {\n-\t\tint err;\n-\n-\t\terr = vmap_range_noflush(addr, addr + (1UL \u003c\u003c page_shift),\n+\t\t\tpage_shift == PAGE_SHIFT) {\n+\t\terr = vmap_small_pages_range_noflush(addr, end, prot, pages);\n+\t} else {\n+\t\tfor (i = 0; i \u003c nr; i += 1U \u003c\u003c (page_shift - PAGE_SHIFT)) {\n+\t\t\terr = vmap_range_noflush(addr,\n+\t\t\t\t\taddr + (1UL \u003c\u003c page_shift),\n \t\t\t\t\tpage_to_phys(pages[i]), prot,\n \t\t\t\t\tpage_shift);\n-\t\tif (err)\n-\t\t\treturn err;\n+\t\t\tif (err)\n+\t\t\t\tbreak;\n \n-\t\taddr += 1UL \u003c\u003c page_shift;\n+\t\t\taddr += 1UL \u003c\u003c page_shift;\n+\t\t}\n \t}\n \n-\treturn 0;\n+\t/* Undo the PTEs installed before the failure. */\n+\tif (err)\n+\t\t__vunmap_range_noflush(start, end,\n+\t\t\t\t       gfpflags_allow_blocking(gfp_mask));\n+\n+\treturn err;\n }\n \n int vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n@@ -738,7 +757,18 @@ int vmap_pages_range_noflush(unsigned long addr, unsigned long end,\n \n \tif (ret)\n \t\treturn ret;\n-\treturn __vmap_pages_range_noflush(addr, end, prot, pages, page_shift);\n+\n+\tret = __vmap_pages_range_noflush(addr, end, prot, pages, page_shift,\n+\t\t\t\t\t gfp_mask);\n+\t/*\n+\t * The page tables undo themselves on failure. Tear down the\n+\t * metadata that was fully set up before the mapping failed.\n+\t */\n+\tif (ret)\n+\t\tkmsan_vunmap_range_noflush(addr, end,\n+\t\t\t\t\t   gfpflags_allow_blocking(gfp_mask));\n+\n+\treturn ret;\n }\n \n static int __vmap_pages_range(unsigned long addr, unsigned long end,\ndiff --git a/mm/vmalloc.h b/mm/vmalloc.h\nindex d8372a4f65c4..9ea28845f713 100644\n--- a/mm/vmalloc.h\n+++ b/mm/vmalloc.h\n@@ -40,10 +40,12 @@ void clear_vm_uninitialized_flag(struct vm_struct *vm);\n \n int __must_check __vmap_pages_range_noflush(unsigned long addr,\n \t\tunsigned long end, pgprot_t prot,\n-\t\tstruct page **pages, unsigned int page_shift);\n+\t\tstruct page **pages, unsigned int page_shift,\n+\t\tgfp_t gfp_mask);\n \n void vunmap_range_noflush(unsigned long start, unsigned long end);\n \n-void __vunmap_range_noflush(unsigned long start, unsigned long end);\n+void __vunmap_range_noflush(unsigned long start, unsigned long end,\n+\t\t\t    bool can_resched);\n \n #endif /* __MM_VMALLOC_H */\n-- \n2.25.1"
}

gemini-3.8-flash

null

null

							input: 26790
							output: 31
							thoughts: 549
						

**Analyzing the Patch Series and Crash Report**

Okay, let's break this down. First, I need to get a handle on what this patch series is about. It seems we're dealing with `mm/vmalloc`, `mm/kmsan`, `mm/percpu-vm`, and `arch/powerpc`, so this is definitely related to memory management, specifically within vmalloc, vmap, and vunmap ranges. The goal is to address issues with partial mapping rollbacks and improve error handling. That's a key area.

Now, let's quickly review those patches individually to refresh the details:

*   Patch 3: Looks like we're clamping an unaligned range in `vunmap_pte_range()`. Okay, aligning things.
*   Patch 4: Propagating errors in `vmap_pages_p*d_range()`. Smart; we don't want to lose those.
*   Patch 5: Rejecting unaligned ranges in `vmap_pages_pte_range()`. Good for safety.
*   Patch 6: Rejecting empty and unaligned ranges in `__vmap_pages_range_noflush()`. Defensive programming.
*   Patch 7: Cache flushing after success, not before. Efficiency is key.
*   Patch 9: Dropping redundant unmaps on failure for powerpc. Optimizing.
*   Patch 10: Stopping the unmap of the CPU that failed. Makes sense.

Alright, with that refresher, I've got a grasp of the context. Next, I need to connect this to the crash report. We've got a "task blocked for more than 143 seconds," which usually indicates a lock contention or deadlock. The call trace points us to `fuse_file_fallocate`, which I need to check out more closely. It looks like it could be related to the `madvise` system call, but the call trace shows the `fuse` filesystem is likely the root of the problem.

My next step is to examine the `fuse_file_fallocate` function and how it interacts with the vmalloc infrastructure, because if there is a blocking state, and `fallocate` or `madvise` is involved, there is a good chance that one of the patches deals with the crash. I'll focus on potential race conditions or lock contention within the `vmalloc` code that could be triggered by `fuse_file_fallocate`. Understanding the interaction between these modules is essential to pinpoint the root cause and determine if the patches are relevant.

{
  "Expression": "fuse_file_fallocate",
  "PathPrefixes": [
    "fs/fuse/"
  ]
}

{
  "Output": "fs/fuse/file.c=2822=static int fuse_writeback_range(struct inode *inode, loff_t start, loff_t end)\n--\nfs/fuse/file.c-2831-\nfs/fuse/file.c:2832:static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,\nfs/fuse/file.c-2833-\t\t\t\tloff_t length)\n--\nfs/fuse/file.c=3076=static const struct file_operations fuse_file_operations = {\n--\nfs/fuse/file.c-3092-\t.poll\t\t= fuse_file_poll,\nfs/fuse/file.c:3093:\t.fallocate\t= fuse_file_fallocate,\nfs/fuse/file.c-3094-\t.copy_file_range = fuse_copy_file_range,\n"
}

gemini-3.8-flash

null

null

							input: 28157
							output: 36
							thoughts: 22
						

Here's my summary, as though I'm thinking through this process:

**Diving into `fuse_file_fallocate`**

Okay, time to get my hands dirty and dissect `fuse_file_fallocate`. Specifically, I'm going to navigate over to `fs/fuse/file.c` to examine its implementation. I need to understand exactly how fallocate operations are handled within the FUSE framework. I'm expecting this to be a crucial function for managing file space allocation and deallocation within a FUSE filesystem, so I'll be looking for nuances in how it interacts with the underlying storage and how it handles potential errors. I'll need to pay close attention to the interaction with the FUSE kernel interface and how it translates fallocate requests into the equivalent operations on the user-space filesystem. I'm anticipating some interesting code in here, potentially involving caching, permission checks, and careful error handling to maintain data consistency. Let's see what we've got!

{
  "File": "fs/fuse/file.c",
  "FirstLine": 2832,
  "LineCount": 40
}

{
  "Contents": "2832:\tstatic long fuse_file_fallocate(struct file *file, int mode, loff_t offset,\n2833:\t\t\t\t\tloff_t length)\n2834:\t{\n2835:\t\tstruct fuse_file *ff = file-\u003eprivate_data;\n2836:\t\tstruct inode *inode = file_inode(file);\n2837:\t\tstruct fuse_inode *fi = get_fuse_inode(inode);\n2838:\t\tstruct fuse_mount *fm = ff-\u003efm;\n2839:\t\tFUSE_ARGS(args);\n2840:\t\tstruct fuse_fallocate_in inarg = {\n2841:\t\t\t.fh = ff-\u003efh,\n2842:\t\t\t.offset = offset,\n2843:\t\t\t.length = length,\n2844:\t\t\t.mode = mode\n2845:\t\t};\n2846:\t\tint err;\n2847:\t\tbool block_faults = FUSE_IS_DAX(inode) \u0026\u0026\n2848:\t\t\t(!(mode \u0026 FALLOC_FL_KEEP_SIZE) ||\n2849:\t\t\t (mode \u0026 (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)));\n2850:\t\n2851:\t\tif (mode \u0026 ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |\n2852:\t\t\t     FALLOC_FL_ZERO_RANGE))\n2853:\t\t\treturn -EOPNOTSUPP;\n2854:\t\n2855:\t\tif (fm-\u003efc-\u003eno_fallocate)\n2856:\t\t\treturn -EOPNOTSUPP;\n2857:\t\n2858:\t\tinode_lock(inode);\n2859:\t\tif (block_faults) {\n2860:\t\t\tfilemap_invalidate_lock(inode-\u003ei_mapping);\n2861:\t\t\terr = fuse_dax_break_layouts(inode, 0, -1);\n2862:\t\t\tif (err)\n2863:\t\t\t\tgoto out;\n2864:\t\t}\n2865:\t\n2866:\t\tif (mode \u0026 (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) {\n2867:\t\t\tloff_t endbyte = offset + length - 1;\n2868:\t\n2869:\t\t\terr = fuse_writeback_range(inode, offset, endbyte);\n2870:\t\t\tif (err)\n2871:\t\t\t\tgoto out;\n"
}

gemini-3.8-flash

null

null

							input: 29071
							output: 264
							thoughts: 1181
						

**Triage Conclusion: FUSE Hung Task - Not Related to Patch Series**

Okay, let's break this down. Line 2858, `inode_lock(inode)`... right, that's `down_write(&inode->i_rwsem)`. And the lock info... I see two tasks from the same `syz.2.1137` process, 10687 and 10683. Task 10687 is trying to grab the inode lock (`#1: ffff88810ffeb240`) – it's stuck in `down_write`, called from `fuse_file_fallocate`.  The slow path is indicating it's waiting, and that's usually bad news.

Now, look at 10683.  It *already* holds that same inode lock in `fuse_file_write_iter`. Bingo! And from the looks of it, it's probably stuck waiting on something, likely the fuse daemon. It is holding the inode lock (i_mutex) while performing a fuse write, so task 10687 will just sit there and eventually the hung task detector kicks in.

Critically, this seems to be a classic FUSE deadlock or hang scenario.  It's a known behavior where operations can block waiting on the userspace daemon or, as it looks like here, each other.

Now, let's confirm the triage steps. First, the crash report: hung task, task 10687 blocked for 143+ seconds.  The stack shows the `rwsem_down_write_slowpath` path, all the way down to `fuse_file_fallocate`, which then involves `madvise_vma_behavior` which is odd but this is not unexpected for a fuse-related issue. The key is the inode lock held by 10683 and the wait by 10687. And we are looking at FUSE inodes.

Second, the patch series: `mm/kmsan and mm/vmalloc fixes`.  Looking at the files modified: `arch/powerpc/*`, `include/linux/kmsan.h`, `mm/kmsan/*`, `mm/percpu-vm.c`, and `mm/vmalloc.*`.  Not a single file, function, or data structure from *this* crash report is touched by that patch series. Absolutely nothing. It's completely unrelated.

Therefore, introduced equals false, and we can say with confidence that this issue is unrelated to the patch series under review. This is likely a known FUSE interaction with syzkaller. Time to set results.

{
  "Introduced": false,
  "Reasoning": "The crash report is a hung task warning (\"task syz.2.1137:10687 blocked for more than 143 seconds\") where task 10687 is blocked in `down_write()` within `fuse_file_fallocate()` called via `madvise(..., MADV_REMOVE)`. The lock it is waiting for is the inode rwsem (`\u0026sb-\u003es_type-\u003ei_mutex_key#31`), which is held by task 10683 executing `fuse_file_write_iter()`. This is a known condition during FUSE fuzzing where FUSE filesystem operations block waiting for responses from the userspace FUSE daemon or become deadlocked.\n\nThe patch series under test only modifies kernel virtual memory mapping/unmapping error-handling logic (`mm/vmalloc.c`, `mm/kmsan/*`, `mm/percpu-vm.c`, and `arch/powerpc/*`). It does not modify FUSE, VFS fallocate/write paths, madvise, or rwsem locking. Therefore, this hung task is completely unrelated to the patch series."
}

{
  "Introduced": false,
  "Reasoning": "The crash report is a hung task warning (\"task syz.2.1137:10687 blocked for more than 143 seconds\") where task 10687 is blocked in `down_write()` within `fuse_file_fallocate()` called via `madvise(..., MADV_REMOVE)`. The lock it is waiting for is the inode rwsem (`\u0026sb-\u003es_type-\u003ei_mutex_key#31`), which is held by task 10683 executing `fuse_file_write_iter()`. This is a known condition during FUSE fuzzing where FUSE filesystem operations block waiting for responses from the userspace FUSE daemon or become deadlocked.\n\nThe patch series under test only modifies kernel virtual memory mapping/unmapping error-handling logic (`mm/vmalloc.c`, `mm/kmsan/*`, `mm/percpu-vm.c`, and `arch/powerpc/*`). It does not modify FUSE, VFS fallocate/write paths, madvise, or rwsem locking. Therefore, this hung task is completely unrelated to the patch series."
}