FAILED: patch "[PATCH] mm, slab: clean up slab->obj_exts always" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x be8250786ca94952a19ce87f98ad9906448bc9ef
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025050521-crispy-study-e836@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From be8250786ca94952a19ce87f98ad9906448bc9ef Mon Sep 17 00:00:00 2001
From: Zhenhua Huang <[email protected]>
Date: Mon, 21 Apr 2025 15:52:32 +0800
Subject: [PATCH] mm, slab: clean up slab->obj_exts always

When memory allocation profiling is disabled at runtime or due to an error, shutdown_mem_profiling() is called: slab->obj_exts which previously allocated remains.
It won't be cleared by unaccount_slab() because of mem_alloc_profiling_enabled() not true. It's incorrect, slab->obj_exts should always be cleaned up in unaccount_slab() to avoid following error:

[...]BUG: Bad page state in process...
..
[...]page dumped because: page still charged to cgroup

index dc9e729e1d26..be8b09e09d30 100644
@@ -2028,8 +2028,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 	return 0;
 }
 
-/* Should be called only if mem_alloc_profiling_enabled() */
-static noinline void free_slab_obj_exts(struct slab *slab)
+static inline void free_slab_obj_exts(struct slab *slab)
 {
 	struct slabobj_ext *obj_exts;
 

@@ -2049,18 +2048,6 @@ static noinline void free_slab_obj_exts(struct slab *slab)
 	slab->obj_exts = 0;
 }
 
-static inline bool need_slab_obj_ext(void)
-{
-	if (mem_alloc_profiling_enabled())
-		return true;
-
-	/*
-	 * CONFIG_MEMCG creates vector of obj_cgroup objects conditionally
-	 * inside memcg_slab_post_alloc_hook. No other users for now.
-	 */
-	return false;
-}
-
 #else /* CONFIG_SLAB_OBJ_EXT */
 
 static inline void init_slab_obj_exts(struct slab *slab)

@@ -2077,11 +2064,6 @@ static inline void free_slab_obj_exts(struct slab *slab)
 {
 }
 
-static inline bool need_slab_obj_ext(void)
-{
-	return false;
-}
-
 #endif /* CONFIG_SLAB_OBJ_EXT */
 
 #ifdef CONFIG_MEM_ALLOC_PROFILING

@@ -2129,7 +2111,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
 static inline void
 alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
 {
-	if (need_slab_obj_ext())
+	if (mem_alloc_profiling_enabled())
 		__alloc_tagging_slab_alloc_hook(s, object, flags);
 }
 

@@ -2601,8 +2583,12 @@ static __always_inline void account_slab(struct slab *slab, int order,
 static __always_inline void unaccount_slab(struct slab *slab, int order,
 					   struct kmem_cache *s)
 {
-	if (memcg_kmem_online() || need_slab_obj_ext())
-		free_slab_obj_exts(slab);
+	/*
+	 * The slab object extensions should now be freed regardless of
+	 * whether mem_alloc_profiling_enabled() or not because profiling
+	 * might have been disabled after slab->obj_exts got allocated.
+	 */
+	free_slab_obj_exts(slab);
 
 	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
 			    -(PAGE_SIZE << order));

From: Zhenhua Huang <[email protected]>

When memory allocation profiling is disabled at runtime or due to an error, shutdown_mem_profiling() is called: slab->obj_exts which previously allocated remains.
It won't be cleared by unaccount_slab() because of mem_alloc_profiling_enabled() not true. It's incorrect, slab->obj_exts should always be cleaned up in unaccount_slab() to avoid following error:

[...]BUG: Bad page state in process...
..
[...]page dumped because: page still charged to cgroup

[surenb: fixed trivial merge conflict in alloc_tagging_slab_alloc_hook(), skipped inlining free_slab_obj_exts() as it's already inline in 6.12]

---
 mm/slub.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

index c26d9cd107cc..66f86e532818 100644
@@ -2035,18 +2035,6 @@ static inline void free_slab_obj_exts(struct slab *slab)
 	slab->obj_exts = 0;
 }
 
-static inline bool need_slab_obj_ext(void)
-{
-	if (mem_alloc_profiling_enabled())
-		return true;
-
-	/*
-	 * CONFIG_MEMCG creates vector of obj_cgroup objects conditionally
-	 * inside memcg_slab_post_alloc_hook. No other users for now.
-	 */
-	return false;
-}
-
 #else /* CONFIG_SLAB_OBJ_EXT */
 
 static inline void init_slab_obj_exts(struct slab *slab)

@@ -2063,11 +2051,6 @@ static inline void free_slab_obj_exts(struct slab *slab)
 {
 }
 
-static inline bool need_slab_obj_ext(void)
-{
-	return false;
-}
-
 #endif /* CONFIG_SLAB_OBJ_EXT */
 
 #ifdef CONFIG_MEM_ALLOC_PROFILING

@@ -2099,7 +2082,7 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
 static inline void
 alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
 {
-	if (need_slab_obj_ext()) {
+	if (mem_alloc_profiling_enabled()) {
 		struct slabobj_ext *obj_exts;
 
 		obj_exts = prepare_slab_obj_exts_hook(s, flags, object);

@@ -2577,8 +2560,12 @@ static __always_inline void account_slab(struct slab *slab, int order,
 static __always_inline void unaccount_slab(struct slab *slab, int order,
 					   struct kmem_cache *s)
 {
-	if (memcg_kmem_online() || need_slab_obj_ext())
-		free_slab_obj_exts(slab);
+	/*
+	 * The slab object extensions should now be freed regardless of
+	 * whether mem_alloc_profiling_enabled() or not because profiling
+	 * might have been disabled after slab->obj_exts got allocated.
+	 */
+	free_slab_obj_exts(slab);
 
 	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
 			    -(PAGE_SIZE << order));

2.49.0.967.g6a0df3ecc3-goog

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
⚠️ Found matching upstream commit but patch is missing proper reference to it

Found matching upstream commit: be8250786ca94952a19ce87f98ad9906448bc9ef

WARNING: Author mismatch between patch and found commit:
Backport author: Suren Baghdasaryan<[email protected]> Commit author: Zhenhua Huang<[email protected]>

Status in newer kernel trees:
6.14.y | Present (different SHA1: 94107e5aed93)

Note: The patch differs from the upstream commit:
---
1: be8250786ca94 ! 1: 86ffacf03afed mm, slab: clean up slab->obj_exts always
@@ Commit message

+ (cherry picked from commit be8250786ca94952a19ce87f98ad9906448bc9ef)
+ [surenb: fixed trivial merge conflict in alloc_tagging_slab_alloc_hook(),
+ skipped inlining free_slab_obj_exts() as it's already inline in 6.12]
+ Signed-off-by: Suren Baghdasaryan <[email protected]>

## mm/slub.c ##
-@@ mm/slub.c: int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
- return 0;
- }
-
--/* Should be called only if mem_alloc_profiling_enabled() */ --static noinline void free_slab_obj_exts(struct slab *slab) -+static inline void free_slab_obj_exts(struct slab *slab)
- {
- struct slabobj_ext *obj_exts;
-
-@@ mm/slub.c: static noinline void free_slab_obj_exts(struct slab *slab) +@@ mm/slub.c: static inline void free_slab_obj_exts(struct slab *slab)
slab->obj_exts = 0;
}

@@ mm/slub.c: static inline void free_slab_obj_exts(struct slab *slab)
#endif /* CONFIG_SLAB_OBJ_EXT */

#ifdef CONFIG_MEM_ALLOC_PROFILING
-@@ mm/slub.c: __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags) +@@ mm/slub.c: prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
static inline void
alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags) {
-- if (need_slab_obj_ext())
-+ if (mem_alloc_profiling_enabled())
- __alloc_tagging_slab_alloc_hook(s, object, flags);
- }
+- if (need_slab_obj_ext()) {
++ if (mem_alloc_profiling_enabled()) {
+ struct slabobj_ext *obj_exts;

+ obj_exts = prepare_slab_obj_exts_hook(s, flags, object);
@@ mm/slub.c: static __always_inline void account_slab(struct slab *slab, int order,
static __always_inline void unaccount_slab(struct slab *slab, int order,
struct kmem_cache *s)
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.12.y       |  Success    |  Success   |

Not sure why "patch is missing proper reference to it". I see (cherry picked from commit be8250786ca94952a19ce87f98ad9906448bc9ef) in place. Did I miss something?

Yep, this is expected as I had to make changes when backporting.

And the changes are documented above.

It tries to find one of the references described in the docs for submitting stuff to stable@:

https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-3

Thanks,
Sasha

Ah, I see now what I missed. Thanks!
Would you be able to add the reference or should I repost the backports?

No need, it's already in the queue for the next round of stable releases in a few hours.

greg k-h