AI Trajectory

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "KMSANReasoning": "",
  "NeedsKMSAN": false,
  "Reasoning": "The patch enhances SLUB debugging (SLAB_STORE_USER) by recording the previous allocation and free stack traces for an object. This is a diagnostic feature used purely for logging during SLUB debug reports and does not functionally alter the core execution flow of the kernel.",
  "WorthFuzzing": false
}

null

{
  "PatchDiff": "commit 93f332ee6cb262c1ca70073e7c2ad8640127ecd8\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Aug 13 17:44:45 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/Documentation/admin-guide/mm/slab.rst b/Documentation/admin-guide/mm/slab.rst\nindex 14429ab90611b..5f60904b1e0ba 100644\n--- a/Documentation/admin-guide/mm/slab.rst\n+++ b/Documentation/admin-guide/mm/slab.rst\n@@ -49,7 +49,8 @@ Possible debug options are::\n \t\t\tSorry SLAB legacy issues)\n \tZ\t\tRed zoning\n \tP\t\tPoisoning (object and padding)\n-\tU\t\tUser tracking (free and alloc)\n+\tU\t\tUser tracking (free and alloc, plus one previous\n+\t\t\tcompleted object lifetime)\n \tT\t\tTrace (please only use on single slabs)\n \tA\t\tEnable failslab filter mark for the cache\n \tO\t\tSwitch debugging off for caches that would have\n@@ -245,10 +246,20 @@ into the syslog:\n \tcpu\u003e pid=\u003cpid of the process\u003e\n      INFO: Freed in \u003ckernel function\u003e age=\u003cjiffies since free\u003e cpu=\u003cfreed by cpu\u003e\n \tpid=\u003cpid of the process\u003e\n+     INFO: Previous object lifetime:\n+     INFO: Allocated in \u003ckernel function\u003e age=\u003cjiffies since alloc\u003e cpu=\u003callocated by\n+\tcpu\u003e pid=\u003cpid of the process\u003e\n+     INFO: Freed in \u003ckernel function\u003e age=\u003cjiffies since free\u003e cpu=\u003cfreed by cpu\u003e\n+\tpid=\u003cpid of the process\u003e\n \n    (Object allocation / free information is only available if SLAB_STORE_USER is\n    set for the slab. slab_debug sets that option)\n \n+   If an object with a completed allocation/free pair is reused, user tracking\n+   also retains that pair as the previous object lifetime. This address history\n+   can help diagnose stale references after reuse, but it does not establish\n+   semantic ownership or identify a use-after-free root cause by itself.\n+\n 2. The object contents if an object was involved.\n \n    Various types of lines can follow the BUG SLUB line:\ndiff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c\nindex fa6d31dbca166..62d0f5e642686 100644\n--- a/lib/tests/slub_kunit.c\n+++ b/lib/tests/slub_kunit.c\n@@ -6,6 +6,7 @@\n #include \u003clinux/module.h\u003e\n #include \u003clinux/kernel.h\u003e\n #include \u003clinux/rcupdate.h\u003e\n+#include \u003clinux/sched.h\u003e\n #include \u003clinux/delay.h\u003e\n #include \u003clinux/perf_event.h\u003e\n #include \"../mm/slab.h\"\n@@ -106,6 +107,38 @@ static void test_first_word(struct kunit *test)\n \tkmem_cache_destroy(s);\n }\n \n+static void test_store_user_previous_lifetime(struct kunit *test)\n+{\n+\tstruct kmem_cache *s;\n+\tvoid *p;\n+\tvoid *q;\n+\n+\ts = test_kmem_cache_create(\"TestSlub_prev_lifetime\", 64,\n+\t\t\t\t   SLAB_STORE_USER | SLAB_NO_MERGE);\n+\tmigrate_disable();\n+\tp = kmem_cache_alloc(s, GFP_KERNEL);\n+\tif (!p) {\n+\t\tKUNIT_FAIL(test, \"failed to allocate the first object\");\n+\t\tgoto out_enable;\n+\t}\n+\tKUNIT_EXPECT_FALSE(test, slab_test_has_previous_lifetime(s, p));\n+\n+\tkmem_cache_free(s, p);\n+\tq = kmem_cache_alloc(s, GFP_KERNEL);\n+\tif (q != p) {\n+\t\tKUNIT_FAIL(test, \"freed object was not immediately reused\");\n+\t\tif (q)\n+\t\t\tkmem_cache_free(s, q);\n+\t\tgoto out_enable;\n+\t}\n+\tKUNIT_EXPECT_TRUE(test, slab_test_has_previous_lifetime(s, q));\n+\n+\tkmem_cache_free(s, q);\n+out_enable:\n+\tmigrate_enable();\n+\tkmem_cache_destroy(s);\n+}\n+\n static void test_clobber_50th_byte(struct kunit *test)\n {\n \tstruct kmem_cache *s = test_kmem_cache_create(\"TestSlub_50th_word_free\",\n@@ -395,6 +428,7 @@ static struct kunit_case test_cases[] = {\n #ifndef CONFIG_KASAN\n \tKUNIT_CASE(test_next_pointer),\n \tKUNIT_CASE(test_first_word),\n+\tKUNIT_CASE(test_store_user_previous_lifetime),\n \tKUNIT_CASE(test_clobber_50th_byte),\n #endif\n \n@@ -419,3 +453,4 @@ kunit_test_suite(test_suite);\n \n MODULE_DESCRIPTION(\"Kunit tests for slub allocator\");\n MODULE_LICENSE(\"GPL\");\n+MODULE_IMPORT_NS(\"EXPORTED_FOR_KUNIT_TESTING\");\ndiff --git a/mm/slab.h b/mm/slab.h\nindex f5e336b6b6b04..15634d9603f8f 100644\n--- a/mm/slab.h\n+++ b/mm/slab.h\n@@ -518,6 +518,10 @@ bool slab_in_kunit_test(void);\n static inline bool slab_in_kunit_test(void) { return false; }\n #endif\n \n+#if IS_ENABLED(CONFIG_SLUB_KUNIT_TEST)\n+bool slab_test_has_previous_lifetime(struct kmem_cache *s, void *object);\n+#endif\n+\n /*\n  * slub is about to manipulate internal object metadata.  This memory lies\n  * outside the range of the allocated object, so accessing it would normally\ndiff --git a/mm/slub.c b/mm/slub.c\nindex 0337e60db5ace..d6b7487fb3003 100644\n--- a/mm/slub.c\n+++ b/mm/slub.c\n@@ -46,6 +46,7 @@\n #include \u003clinux/prandom.h\u003e\n #include \u003ckunit/test.h\u003e\n #include \u003ckunit/test-bug.h\u003e\n+#include \u003ckunit/visibility.h\u003e\n #include \u003clinux/sort.h\u003e\n #include \u003clinux/irq_work.h\u003e\n #include \u003clinux/kprobes.h\u003e\n@@ -329,7 +330,13 @@ struct track {\n \tunsigned long when;\t/* When did the operation occur */\n };\n \n-enum track_item { TRACK_ALLOC, TRACK_FREE };\n+enum track_item {\n+\tTRACK_ALLOC,\n+\tTRACK_FREE,\n+\tTRACK_PREV_ALLOC,\n+\tTRACK_PREV_FREE,\n+\tTRACK_NR,\n+};\n \n #ifdef SLAB_SUPPORTS_SYSFS\n static int sysfs_slab_add(struct kmem_cache *);\n@@ -753,7 +760,7 @@ static inline void set_orig_size(struct kmem_cache *s,\n \t\treturn;\n \n \tp += get_info_end(s);\n-\tp += sizeof(struct track) * 2;\n+\tp += sizeof(struct track) * TRACK_NR;\n \n \t*(unsigned long *)p = orig_size;\n }\n@@ -769,7 +776,7 @@ static inline unsigned long get_orig_size(struct kmem_cache *s, void *object)\n \t\treturn s-\u003eobject_size;\n \n \tp += get_info_end(s);\n-\tp += sizeof(struct track) * 2;\n+\tp += sizeof(struct track) * TRACK_NR;\n \n \treturn *(unsigned long *)p;\n }\n@@ -887,7 +894,7 @@ static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)\n \tunsigned int offset = get_info_end(s);\n \n \tif (kmem_cache_debug_flags(s, SLAB_STORE_USER))\n-\t\toffset += sizeof(struct track) * 2;\n+\t\toffset += sizeof(struct track) * TRACK_NR;\n \n \tif (slub_debug_orig_size(s))\n \t\toffset += sizeof(unsigned long);\n@@ -1074,12 +1081,23 @@ static void set_track_update(struct kmem_cache *s, void *object,\n \tp-\u003ewhen = jiffies;\n }\n \n-static __always_inline void set_track(struct kmem_cache *s, void *object,\n-\t\t\t\t      enum track_item alloc, unsigned long addr, gfp_t gfp_flags)\n+static __always_inline void set_alloc_track(struct kmem_cache *s, void *object,\n+\t\t\t\t\t    unsigned long addr, gfp_t gfp_flags)\n {\n \tdepot_stack_handle_t handle = set_track_prepare(gfp_flags);\n+\tstruct track *alloc = get_track(s, object, TRACK_ALLOC);\n+\tstruct track *free = get_track(s, object, TRACK_FREE);\n+\tstruct track *prev_alloc;\n+\tstruct track *prev_free;\n+\n+\tif (alloc-\u003eaddr \u0026\u0026 free-\u003eaddr) {\n+\t\tprev_alloc = get_track(s, object, TRACK_PREV_ALLOC);\n+\t\tprev_free = get_track(s, object, TRACK_PREV_FREE);\n+\t\t*prev_alloc = *alloc;\n+\t\t*prev_free = *free;\n+\t}\n \n-\tset_track_update(s, object, alloc, addr, handle);\n+\tset_track_update(s, object, TRACK_ALLOC, addr, handle);\n }\n \n static void init_tracking(struct kmem_cache *s, void *object)\n@@ -1090,7 +1108,7 @@ static void init_tracking(struct kmem_cache *s, void *object)\n \t\treturn;\n \n \tp = get_track(s, object, TRACK_ALLOC);\n-\tmemset(p, 0, 2*sizeof(struct track));\n+\tmemset(p, 0, sizeof(struct track) * TRACK_NR);\n }\n \n static void print_track(const char *s, struct track *t, unsigned long pr_time)\n@@ -1113,14 +1131,33 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time)\n \n void print_tracking(struct kmem_cache *s, void *object)\n {\n+\tstruct track *prev_alloc;\n \tunsigned long pr_time = jiffies;\n+\n \tif (!(s-\u003eflags \u0026 SLAB_STORE_USER))\n \t\treturn;\n \n \tprint_track(\"Allocated\", get_track(s, object, TRACK_ALLOC), pr_time);\n \tprint_track(\"Freed\", get_track(s, object, TRACK_FREE), pr_time);\n+\n+\tprev_alloc = get_track(s, object, TRACK_PREV_ALLOC);\n+\tif (!prev_alloc-\u003eaddr)\n+\t\treturn;\n+\n+\tpr_err(\"Previous object lifetime:\\n\");\n+\tprint_track(\"Allocated\", prev_alloc, pr_time);\n+\tprint_track(\"Freed\", get_track(s, object, TRACK_PREV_FREE), pr_time);\n }\n \n+#if IS_ENABLED(CONFIG_SLUB_KUNIT_TEST)\n+bool slab_test_has_previous_lifetime(struct kmem_cache *s, void *object)\n+{\n+\treturn get_track(s, object, TRACK_PREV_ALLOC)-\u003eaddr \u0026\u0026\n+\t       get_track(s, object, TRACK_PREV_FREE)-\u003eaddr;\n+}\n+EXPORT_SYMBOL_IF_KUNIT(slab_test_has_previous_lifetime);\n+#endif\n+\n static void print_slab_info(const struct slab *slab)\n {\n \tpr_err(\"Slab 0x%p objects=%u used=%u fp=0x%p flags=%pGp\\n\",\n@@ -1199,7 +1236,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)\n \toff = get_info_end(s);\n \n \tif (s-\u003eflags \u0026 SLAB_STORE_USER)\n-\t\toff += 2 * sizeof(struct track);\n+\t\toff += sizeof(struct track) * TRACK_NR;\n \n \tif (slub_debug_orig_size(s))\n \t\toff += sizeof(unsigned long);\n@@ -1366,8 +1403,8 @@ check_bytes_and_report(struct kmem_cache *s, struct slab *slab,\n  *\n  * [Metadata starts at object + s-\u003einuse]\n  *   - A. freelist pointer (if freeptr_outside_object)\n- *   - B. alloc tracking (SLAB_STORE_USER)\n- *   - C. free tracking (SLAB_STORE_USER)\n+ *   - B. current alloc/free tracking (SLAB_STORE_USER)\n+ *   - C. previous alloc/free tracking (SLAB_STORE_USER)\n  *   - D. original request size (SLAB_KMALLOC \u0026\u0026 SLAB_STORE_USER)\n  *   - E. KASAN metadata (if enabled)\n  *\n@@ -1403,7 +1440,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)\n \n \tif (s-\u003eflags \u0026 SLAB_STORE_USER) {\n \t\t/* We also have user information there */\n-\t\toff += 2 * sizeof(struct track);\n+\t\toff += sizeof(struct track) * TRACK_NR;\n \n \t\tif (s-\u003eflags \u0026 SLAB_KMALLOC)\n \t\t\toff += sizeof(unsigned long);\n@@ -2024,8 +2061,8 @@ static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}\n static inline int check_object(struct kmem_cache *s, struct slab *slab,\n \t\t\tvoid *object, u8 val) { return 1; }\n static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags) { return 0; }\n-static inline void set_track(struct kmem_cache *s, void *object,\n-\t\t\t     enum track_item alloc, unsigned long addr, gfp_t gfp_flags) {}\n+static inline void set_alloc_track(struct kmem_cache *s, void *object,\n+\t\t\t\t   unsigned long addr, gfp_t gfp_flags) {}\n static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,\n \t\t\t\t\tstruct slab *slab) {}\n static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,\n@@ -4493,7 +4530,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,\n \n success:\n \tif (kmem_cache_debug_flags(s, SLAB_STORE_USER))\n-\t\tset_track(s, object, TRACK_ALLOC, ac-\u003ecaller_addr, gfpflags);\n+\t\tset_alloc_track(s, object, ac-\u003ecaller_addr, gfpflags);\n \n \treturn object;\n }\n@@ -7895,7 +7932,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)\n \t\t * Need to store information about allocs and frees after\n \t\t * the object.\n \t\t */\n-\t\tsize += 2 * sizeof(struct track);\n+\t\tsize += sizeof(struct track) * TRACK_NR;\n \n \t\t/* Save the original kmalloc request size */\n \t\tif (flags \u0026 SLAB_KMALLOC)\n"
}

best-expensive

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch enhances SLUB debugging (SLAB_STORE_USER) by recording the previous allocation and free stack traces for an object. This is a diagnostic feature used purely for logging during SLUB debug reports and does not functionally alter the core execution flow of the kernel.",
  "WorthFuzzing": false
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
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.

For your convenience, here is the diff of the changes:
commit 93f332ee6cb262c1ca70073e7c2ad8640127ecd8
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Aug 13 17:44:45 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/admin-guide/mm/slab.rst b/Documentation/admin-guide/mm/slab.rst
index 14429ab90611b..5f60904b1e0ba 100644
--- a/Documentation/admin-guide/mm/slab.rst
+++ b/Documentation/admin-guide/mm/slab.rst
@@ -49,7 +49,8 @@ Possible debug options are::
 			Sorry SLAB legacy issues)
 	Z		Red zoning
 	P		Poisoning (object and padding)
-	U		User tracking (free and alloc)
+	U		User tracking (free and alloc, plus one previous
+			completed object lifetime)
 	T		Trace (please only use on single slabs)
 	A		Enable failslab filter mark for the cache
 	O		Switch debugging off for caches that would have
@@ -245,10 +246,20 @@ into the syslog:
 	cpu> pid=<pid of the process>
      INFO: Freed in <kernel function> age=<jiffies since free> cpu=<freed by cpu>
 	pid=<pid of the process>
+     INFO: Previous object lifetime:
+     INFO: Allocated in <kernel function> age=<jiffies since alloc> cpu=<allocated by
+	cpu> pid=<pid of the process>
+     INFO: Freed in <kernel function> age=<jiffies since free> cpu=<freed by cpu>
+	pid=<pid of the process>
 
    (Object allocation / free information is only available if SLAB_STORE_USER is
    set for the slab. slab_debug sets that option)
 
+   If an object with a completed allocation/free pair is reused, user tracking
+   also retains that pair as the previous object lifetime. This address history
+   can help diagnose stale references after reuse, but it does not establish
+   semantic ownership or identify a use-after-free root cause by itself.
+
 2. The object contents if an object was involved.
 
    Various types of lines can follow the BUG SLUB line:
diff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c
index fa6d31dbca166..62d0f5e642686 100644
--- a/lib/tests/slub_kunit.c
+++ b/lib/tests/slub_kunit.c
@@ -6,6 +6,7 @@
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/rcupdate.h>
+#include <linux/sched.h>
 #include <linux/delay.h>
 #include <linux/perf_event.h>
 #include "../mm/slab.h"
@@ -106,6 +107,38 @@ static void test_first_word(struct kunit *test)
 	kmem_cache_destroy(s);
 }
 
+static void test_store_user_previous_lifetime(struct kunit *test)
+{
+	struct kmem_cache *s;
+	void *p;
+	void *q;
+
+	s = test_kmem_cache_create("TestSlub_prev_lifetime", 64,
+				   SLAB_STORE_USER | SLAB_NO_MERGE);
+	migrate_disable();
+	p = kmem_cache_alloc(s, GFP_KERNEL);
+	if (!p) {
+		KUNIT_FAIL(test, "failed to allocate the first object");
+		goto out_enable;
+	}
+	KUNIT_EXPECT_FALSE(test, slab_test_has_previous_lifetime(s, p));
+
+	kmem_cache_free(s, p);
+	q = kmem_cache_alloc(s, GFP_KERNEL);
+	if (q != p) {
+		KUNIT_FAIL(test, "freed object was not immediately reused");
+		if (q)
+			kmem_cache_free(s, q);
+		goto out_enable;
+	}
+	KUNIT_EXPECT_TRUE(test, slab_test_has_previous_lifetime(s, q));
+
+	kmem_cache_free(s, q);
+out_enable:
+	migrate_enable();
+	kmem_cache_destroy(s);
+}
+
 static void test_clobber_50th_byte(struct kunit *test)
 {
 	struct kmem_cache *s = test_kmem_cache_create("TestSlub_50th_word_free",
@@ -395,6 +428,7 @@ static struct kunit_case test_cases[] = {
 #ifndef CONFIG_KASAN
 	KUNIT_CASE(test_next_pointer),
 	KUNIT_CASE(test_first_word),
+	KUNIT_CASE(test_store_user_previous_lifetime),
 	KUNIT_CASE(test_clobber_50th_byte),
 #endif
 
@@ -419,3 +453,4 @@ kunit_test_suite(test_suite);
 
 MODULE_DESCRIPTION("Kunit tests for slub allocator");
 MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
diff --git a/mm/slab.h b/mm/slab.h
index f5e336b6b6b04..15634d9603f8f 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -518,6 +518,10 @@ bool slab_in_kunit_test(void);
 static inline bool slab_in_kunit_test(void) { return false; }
 #endif
 
+#if IS_ENABLED(CONFIG_SLUB_KUNIT_TEST)
+bool slab_test_has_previous_lifetime(struct kmem_cache *s, void *object);
+#endif
+
 /*
  * slub is about to manipulate internal object metadata.  This memory lies
  * outside the range of the allocated object, so accessing it would normally
diff --git a/mm/slub.c b/mm/slub.c
index 0337e60db5ace..d6b7487fb3003 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -46,6 +46,7 @@
 #include <linux/prandom.h>
 #include <kunit/test.h>
 #include <kunit/test-bug.h>
+#include <kunit/visibility.h>
 #include <linux/sort.h>
 #include <linux/irq_work.h>
 #include <linux/kprobes.h>
@@ -329,7 +330,13 @@ struct track {
 	unsigned long when;	/* When did the operation occur */
 };
 
-enum track_item { TRACK_ALLOC, TRACK_FREE };
+enum track_item {
+	TRACK_ALLOC,
+	TRACK_FREE,
+	TRACK_PREV_ALLOC,
+	TRACK_PREV_FREE,
+	TRACK_NR,
+};
 
 #ifdef SLAB_SUPPORTS_SYSFS
 static int sysfs_slab_add(struct kmem_cache *);
@@ -753,7 +760,7 @@ static inline void set_orig_size(struct kmem_cache *s,
 		return;
 
 	p += get_info_end(s);
-	p += sizeof(struct track) * 2;
+	p += sizeof(struct track) * TRACK_NR;
 
 	*(unsigned long *)p = orig_size;
 }
@@ -769,7 +776,7 @@ static inline unsigned long get_orig_size(struct kmem_cache *s, void *object)
 		return s->object_size;
 
 	p += get_info_end(s);
-	p += sizeof(struct track) * 2;
+	p += sizeof(struct track) * TRACK_NR;
 
 	return *(unsigned long *)p;
 }
@@ -887,7 +894,7 @@ static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)
 	unsigned int offset = get_info_end(s);
 
 	if (kmem_cache_debug_flags(s, SLAB_STORE_USER))
-		offset += sizeof(struct track) * 2;
+		offset += sizeof(struct track) * TRACK_NR;
 
 	if (slub_debug_orig_size(s))
 		offset += sizeof(unsigned long);
@@ -1074,12 +1081,23 @@ static void set_track_update(struct kmem_cache *s, void *object,
 	p->when = jiffies;
 }
 
-static __always_inline void set_track(struct kmem_cache *s, void *object,
-				      enum track_item alloc, unsigned long addr, gfp_t gfp_flags)
+static __always_inline void set_alloc_track(struct kmem_cache *s, void *object,
+					    unsigned long addr, gfp_t gfp_flags)
 {
 	depot_stack_handle_t handle = set_track_prepare(gfp_flags);
+	struct track *alloc = get_track(s, object, TRACK_ALLOC);
+	struct track *free = get_track(s, object, TRACK_FREE);
+	struct track *prev_alloc;
+	struct track *prev_free;
+
+	if (alloc->addr && free->addr) {
+		prev_alloc = get_track(s, object, TRACK_PREV_ALLOC);
+		prev_free = get_track(s, object, TRACK_PREV_FREE);
+		*prev_alloc = *alloc;
+		*prev_free = *free;
+	}
 
-	set_track_update(s, object, alloc, addr, handle);
+	set_track_update(s, object, TRACK_ALLOC, addr, handle);
 }
 
 static void init_tracking(struct kmem_cache *s, void *object)
@@ -1090,7 +1108,7 @@ static void init_tracking(struct kmem_cache *s, void *object)
 		return;
 
 	p = get_track(s, object, TRACK_ALLOC);
-	memset(p, 0, 2*sizeof(struct track));
+	memset(p, 0, sizeof(struct track) * TRACK_NR);
 }
 
 static void print_track(const char *s, struct track *t, unsigned long pr_time)
@@ -1113,14 +1131,33 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time)
 
 void print_tracking(struct kmem_cache *s, void *object)
 {
+	struct track *prev_alloc;
 	unsigned long pr_time = jiffies;
+
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
 	print_track("Allocated", get_track(s, object, TRACK_ALLOC), pr_time);
 	print_track("Freed", get_track(s, object, TRACK_FREE), pr_time);
+
+	prev_alloc = get_track(s, object, TRACK_PREV_ALLOC);
+	if (!prev_alloc->addr)
+		return;
+
+	pr_err("Previous object lifetime:\n");
+	print_track("Allocated", prev_alloc, pr_time);
+	print_track("Freed", get_track(s, object, TRACK_PREV_FREE), pr_time);
 }
 
+#if IS_ENABLED(CONFIG_SLUB_KUNIT_TEST)
+bool slab_test_has_previous_lifetime(struct kmem_cache *s, void *object)
+{
+	return get_track(s, object, TRACK_PREV_ALLOC)->addr &&
+	       get_track(s, object, TRACK_PREV_FREE)->addr;
+}
+EXPORT_SYMBOL_IF_KUNIT(slab_test_has_previous_lifetime);
+#endif
+
 static void print_slab_info(const struct slab *slab)
 {
 	pr_err("Slab 0x%p objects=%u used=%u fp=0x%p flags=%pGp\n",
@@ -1199,7 +1236,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
 	off = get_info_end(s);
 
 	if (s->flags & SLAB_STORE_USER)
-		off += 2 * sizeof(struct track);
+		off += sizeof(struct track) * TRACK_NR;
 
 	if (slub_debug_orig_size(s))
 		off += sizeof(unsigned long);
@@ -1366,8 +1403,8 @@ check_bytes_and_report(struct kmem_cache *s, struct slab *slab,
  *
  * [Metadata starts at object + s->inuse]
  *   - A. freelist pointer (if freeptr_outside_object)
- *   - B. alloc tracking (SLAB_STORE_USER)
- *   - C. free tracking (SLAB_STORE_USER)
+ *   - B. current alloc/free tracking (SLAB_STORE_USER)
+ *   - C. previous alloc/free tracking (SLAB_STORE_USER)
  *   - D. original request size (SLAB_KMALLOC && SLAB_STORE_USER)
  *   - E. KASAN metadata (if enabled)
  *
@@ -1403,7 +1440,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
 
 	if (s->flags & SLAB_STORE_USER) {
 		/* We also have user information there */
-		off += 2 * sizeof(struct track);
+		off += sizeof(struct track) * TRACK_NR;
 
 		if (s->flags & SLAB_KMALLOC)
 			off += sizeof(unsigned long);
@@ -2024,8 +2061,8 @@ static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
 static inline int check_object(struct kmem_cache *s, struct slab *slab,
 			void *object, u8 val) { return 1; }
 static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags) { return 0; }
-static inline void set_track(struct kmem_cache *s, void *object,
-			     enum track_item alloc, unsigned long addr, gfp_t gfp_flags) {}
+static inline void set_alloc_track(struct kmem_cache *s, void *object,
+				   unsigned long addr, gfp_t gfp_flags) {}
 static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
 					struct slab *slab) {}
 static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,
@@ -4493,7 +4530,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 
 success:
 	if (kmem_cache_debug_flags(s, SLAB_STORE_USER))
-		set_track(s, object, TRACK_ALLOC, ac->caller_addr, gfpflags);
+		set_alloc_track(s, object, ac->caller_addr, gfpflags);
 
 	return object;
 }
@@ -7895,7 +7932,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
 		 * Need to store information about allocs and frees after
 		 * the object.
 		 */
-		size += 2 * sizeof(struct track);
+		size += sizeof(struct track) * TRACK_NR;
 
 		/* Save the original kmalloc request size */
 		if (flags & SLAB_KMALLOC)

gemini-3.1-pro-preview

null

null

							input: 5815
							output: 85
							thoughts: 884
						

**WorthFuzzing Assessment: SLUB Debugging Patch**

Okay, let's break this down. We have a patch that's tweaking the SLUB debugging features, specifically the SLAB_STORE_USER functionality. It's adding some new tracking mechanisms (`TRACK_PREV_ALLOC`, `TRACK_PREV_FREE`), essentially storing the history of an object's lifetime – allocation and free events. The code modifies `set_alloc_track` to copy this historical data and it adjusts `print_tracking` to output the results. There's also a new KUnit test, `test_store_user_previous_lifetime`, to validate the changes.

My initial thought is, does this warrant fuzzing? It *is* touching the kernel's memory management, so there's always a concern. However, upon deeper inspection, I see that the core function is not changed. The patch introduces changes to metadata size by adding `size += sizeof(struct track) * TRACK_NR;` when `SLAB_STORE_USER` is enabled, but its effect is only related to debugging or diagnostics. The crux of it is storing and printing more information for debugging purposes. This is the addition of an extra data structure with a new structure to record allocation history.

Reading the instructions, it directs me to return `WorthFuzzing=false` if the patch has modifications restricted to Documentation, Kconfig files, code comments, or if it has "purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints." It specifically excludes changes to the execution flow.

Now, let's be honest. This patch isn't *purely* decorative, it modifies data structure in the kernel. But, the modifications only have an effect related to debugging, logging, and crash reports. The previous allocation data is *only* recorded for debugging output. So it’s essentially collecting extra data for logging purposes. It does change the memory layout, but that change is only effective when the debugging feature is enabled.

Looking at `set_alloc_track`, it's just copying the `struct track` data around. The KUnit test only validates the expected results of the added features, and `slab_test_has_previous_lifetime` is just there for testing. There's no major functional shift here, no new core capabilities, just enhanced diagnostic capabilities. No other functionality is altered.

Given the criteria – it's primarily a diagnostic enhancement that alters memory layout only when the debugging feature is enabled – and with the instructions in mind, I think this is a clear case for `WorthFuzzing=false`. It's a debugging feature that simply records and prints extra stack traces. It doesn't modify the core execution flow. So, I will set `WorthFuzzing=false`.

{
  "EnableConfigs": [],
  "FocusSymbols": [],
  "Reasoning": "The patch enhances SLUB debugging (SLAB_STORE_USER) by recording the previous allocation and free stack traces for an object. This is a diagnostic feature used purely for logging during SLUB debug reports and does not functionally alter the core execution flow of the kernel.",
  "WorthFuzzing": false
}

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch enhances SLUB debugging (SLAB_STORE_USER) by recording the previous allocation and free stack traces for an object. This is a diagnostic feature used purely for logging during SLUB debug reports and does not functionally alter the core execution flow of the kernel.",
  "WorthFuzzing": false
}

{
  "WorthFuzzing": false
}

null