[PATCH 0/2] fixes for slab->obj_exts allocation failure handling

[PATCH 0/2] fixes for slab->obj_exts allocation failure handling

[Suren Baghdasaryan]

Fixes for several issues noticed by Shakeel pertaining to slab->obj_exts
allocation failure handling in [1].

Patchset is based on mm-new.

Please route it via vbabka/slab.git as it's relevant to Alexei's patches
in that branch.

[1] https://lore.kernel.org/all/jftidhymri2af5u3xtcqry3cfu6aqzte3uzlznhlaylgrdztsi@5vpjnzpsemf5/

Suren Baghdasaryan (2):
  slab: prevent warnings when slab obj_exts vector allocation fails
  slab: mark slab->obj_exts allocation failures unconditionally

 mm/slab.h | 8 ++++++--
 mm/slub.c | 3 +--
 2 files changed, 7 insertions(+), 4 deletions(-)


base-commit: 9a9318f95d63805868bd21e1381d68c3a75d03a7
-- 
2.51.0.384.g4c02a37b29-goog

[PATCH 1/2] slab: prevent warnings when slab obj_exts vector allocation fails

[Suren Baghdasaryan]

When object extension vector allocation fails, we set slab->obj_exts to
OBJEXTS_ALLOC_FAIL to indicate the failure. Later, once the vector is
successfully allocated, we will use this flag to mark codetag references
stored in that vector as empty to avoid codetag warnings.

slab_obj_exts() used to retrieve the slab->obj_exts vector pointer checks
slab->obj_exts for being either NULL or a pointer with MEMCG_DATA_OBJEXTS
bit set. However it does not handle the case when slab->obj_exts equals
OBJEXTS_ALLOC_FAIL. Add the missing condition to avoid extra warning.

Fixes: 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations")
Reported-by: Shakeel Butt <shakeel.butt@linux.dev>
Closes: https://lore.kernel.org/all/jftidhymri2af5u3xtcqry3cfu6aqzte3uzlznhlaylgrdztsi@5vpjnzpsemf5/
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org # v6.10+
---
 mm/slab.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index c41a512dd07c..b930193fd94e 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -526,8 +526,12 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
 	unsigned long obj_exts = READ_ONCE(slab->obj_exts);
 
 #ifdef CONFIG_MEMCG
-	VM_BUG_ON_PAGE(obj_exts && !(obj_exts & MEMCG_DATA_OBJEXTS),
-							slab_page(slab));
+	/*
+	 * obj_exts should be either NULL, a valid pointer with
+	 * MEMCG_DATA_OBJEXTS bit set or be equal to OBJEXTS_ALLOC_FAIL.
+	 */
+	VM_BUG_ON_PAGE(obj_exts && !(obj_exts & MEMCG_DATA_OBJEXTS) &&
+		       obj_exts != OBJEXTS_ALLOC_FAIL, slab_page(slab));
 	VM_BUG_ON_PAGE(obj_exts & MEMCG_DATA_KMEM, slab_page(slab));
 #endif
 	return (struct slabobj_ext *)(obj_exts & ~OBJEXTS_FLAGS_MASK);
-- 
2.51.0.384.g4c02a37b29-goog

Re: [PATCH 1/2] slab: prevent warnings when slab obj_exts vector allocation fails

[Shakeel Butt]

On Mon, Sep 15, 2025 at 01:09:17PM -0700, Suren Baghdasaryan wrote:
> When object extension vector allocation fails, we set slab->obj_exts to
> OBJEXTS_ALLOC_FAIL to indicate the failure. Later, once the vector is
> successfully allocated, we will use this flag to mark codetag references
> stored in that vector as empty to avoid codetag warnings.
> 
> slab_obj_exts() used to retrieve the slab->obj_exts vector pointer checks
> slab->obj_exts for being either NULL or a pointer with MEMCG_DATA_OBJEXTS
> bit set. However it does not handle the case when slab->obj_exts equals
> OBJEXTS_ALLOC_FAIL. Add the missing condition to avoid extra warning.
> 
> Fixes: 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations")
> Reported-by: Shakeel Butt <shakeel.butt@linux.dev>
> Closes: https://lore.kernel.org/all/jftidhymri2af5u3xtcqry3cfu6aqzte3uzlznhlaylgrdztsi@5vpjnzpsemf5/
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Cc: stable@vger.kernel.org # v6.10+

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

[PATCH 2/2] slab: mark slab->obj_exts allocation failures unconditionally

[Suren Baghdasaryan]

alloc_slab_obj_exts() should mark failed obj_exts vector allocations
independent on whether the vector is being allocated for a new or an
existing slab. Current implementation skips doing this for existing
slabs. Fix this by marking failed allocations unconditionally.

Fixes: 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations")
Reported-by: Shakeel Butt <shakeel.butt@linux.dev>
Closes: https://lore.kernel.org/all/avhakjldsgczmq356gkwmvfilyvf7o6temvcmtt5lqd4fhp5rk@47gp2ropyixg/
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org # v6.10+
---
 mm/slub.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index af343ca570b5..cab4e7822393 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2029,8 +2029,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 			   slab_nid(slab));
 	if (!vec) {
 		/* Mark vectors which failed to allocate */
-		if (new_slab)
-			mark_failed_objexts_alloc(slab);
+		mark_failed_objexts_alloc(slab);
 
 		return -ENOMEM;
 	}
-- 
2.51.0.384.g4c02a37b29-goog

Re: [PATCH 2/2] slab: mark slab->obj_exts allocation failures unconditionally

[Shakeel Butt]

On Mon, Sep 15, 2025 at 01:09:18PM -0700, Suren Baghdasaryan wrote:
> alloc_slab_obj_exts() should mark failed obj_exts vector allocations
> independent on whether the vector is being allocated for a new or an
> existing slab. Current implementation skips doing this for existing
> slabs. Fix this by marking failed allocations unconditionally.
> 
> Fixes: 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations")
> Reported-by: Shakeel Butt <shakeel.butt@linux.dev>
> Closes: https://lore.kernel.org/all/avhakjldsgczmq356gkwmvfilyvf7o6temvcmtt5lqd4fhp5rk@47gp2ropyixg/
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Cc: stable@vger.kernel.org # v6.10+

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH 0/2] fixes for slab->obj_exts allocation failure handling

[Vlastimil Babka]

On 9/15/25 22:09, Suren Baghdasaryan wrote:
> Fixes for several issues noticed by Shakeel pertaining to slab->obj_exts
> allocation failure handling in [1].
> 
> Patchset is based on mm-new.
> 
> Please route it via vbabka/slab.git as it's relevant to Alexei's patches
> in that branch.

Thanks, added to slab/for-6.18/fixes

> [1] https://lore.kernel.org/all/jftidhymri2af5u3xtcqry3cfu6aqzte3uzlznhlaylgrdztsi@5vpjnzpsemf5/
> 
> Suren Baghdasaryan (2):
>   slab: prevent warnings when slab obj_exts vector allocation fails
>   slab: mark slab->obj_exts allocation failures unconditionally
> 
>  mm/slab.h | 8 ++++++--
>  mm/slub.c | 3 +--
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> 
> base-commit: 9a9318f95d63805868bd21e1381d68c3a75d03a7