ntfs_check_logfile() calls kmap_local_folio() on every iteration of its search loop but kunmap_local() only once per folio. The loop visits positions 0, 512, 1024, 2048, 4096 and so on. With 4 KiB pages the first four are in one page, so a mount whose first LogFile folio is in highmem leaves three entries on the kmap_local stack of the mounting task. Kernels without HIGHMEM are not affected. The leaked entries keep migration disabled. nr_pinned of the runqueue the mount ran on stays raised after the task exits, so taking that CPU offline blocks forever in balance_hotplug_wait(). The fifth mount in one task reaches KM_MAX_IDX (12 leaked entries plus 4 in the loop) and hits the BUG_ON() in kmap_local_idx_push(): kernel BUG at mm/highmem.c:480! On x86-32 the generic entry code also warns on return to user space: DEBUG_LOCKS_WARN_ON(current->kmap_ctrl.idx) WARNING: include/linux/highmem-internal.h:17 at __do_fast_syscall_32+0x21e/0x550 Map each page once, when it is read, and unmap that address. Fixes: 5218cd102aec ("ntfs: update misc operations") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter --- Tested in QEMU on top of patch 1 with a fresh mkntfs volume, on the ARM and x86-32 kernels described there. ARM and x86-32 behave the same in all three tests. - One mount on CPU 1 with taskset, then writing 0 to /sys/devices/system/cpu/cpu1/online: without this patch the write was still blocked after 60 seconds and new ssh logins hung. With it CPU 1 goes offline. The same write before the mount works on both kernels. - A program that calls mount(2) and umount(2) eight times in one process: without this patch mounts one to four succeed and the fifth hits the BUG_ON() in kmap_local_idx_push(). With it all eight complete. - Three mounts in a row with mount(8) are clean. x86-32 no longer warns when mount(2) returns. fs/ntfs/logfile.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/fs/ntfs/logfile.c b/fs/ntfs/logfile.c index 1404664dacc0..ce38ce87f8fc 100644 --- a/fs/ntfs/logfile.c +++ b/fs/ntfs/logfile.c @@ -457,7 +457,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) struct ntfs_volume *vol = NTFS_SB(log_vi->i_sb); struct address_space *mapping = log_vi->i_mapping; struct folio *folio = NULL; - u8 *kaddr = NULL; + u8 *kaddr = NULL, *kbase = NULL; struct restart_page_header *rstr1_ph = NULL; struct restart_page_header *rstr2_ph = NULL; int log_page_size, err; @@ -511,7 +511,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) if (!folio || folio->index != idx) { if (folio) { - kunmap_local(kaddr); + kunmap_local(kbase); folio_put(folio); } folio = read_mapping_folio(mapping, idx, NULL); @@ -520,8 +520,9 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) idx); goto err_out; } + kbase = kmap_local_folio(folio, 0); } - kaddr = (u8 *)kmap_local_folio(folio, 0) + (pos & ~PAGE_MASK); + kaddr = kbase + (pos & ~PAGE_MASK); /* * A non-empty block means the logfile is not empty while an * empty block after a non-empty block has been encountered @@ -574,7 +575,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) * find a valid one further in the file. */ if (err != -EINVAL) { - kunmap_local(kaddr); + kunmap_local(kbase); folio_put(folio); goto err_out; } @@ -583,7 +584,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) pos = NTFS_BLOCK_SIZE >> 1; } if (folio) { - kunmap_local(kaddr); + kunmap_local(kbase); folio_put(folio); } if (logfile_is_empty) { -- 2.53.0