From: Vlastimil Babka Date: Thu, 23 Oct 2025 12:01:07 +0000 (+0200) Subject: slab: fix slab accounting imbalance due to defer_deactivate_slab() X-Git-Tag: v6.18-rc3~22^2~1 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=eecd7cb64178efb35f89aa5134cf6ce36c0c66db;p=thirdparty%2Fkernel%2Flinux.git slab: fix slab accounting imbalance due to defer_deactivate_slab() Since commit af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") there's a possibility in alloc_single_from_new_slab() that we discard the newly allocated slab if we can't spin and we fail to trylock. As a result we don't perform inc_slabs_node() later in the function. Instead we perform a deferred deactivate_slab() which can either put the unacounted slab on partial list, or discard it immediately while performing dec_slabs_node(). Either way will cause an accounting imbalance. Fix this by not marking the slab as frozen, and using free_slab() instead of deactivate_slab() for non-frozen slabs in free_deferred_objects(). For CONFIG_SLUB_TINY, that's the only possible case. By not using discard_slab() we avoid dec_slabs_node(). Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Link: https://patch.msgid.link/20251023-fix-slab-accounting-v2-1-0e62d50986ea@suse.cz Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- diff --git a/mm/slub.c b/mm/slub.c index 23d8f54e9486..87a1d2f9de0d 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3422,7 +3422,6 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s, struct slab *slab, if (!allow_spin && !spin_trylock_irqsave(&n->list_lock, flags)) { /* Unlucky, discard newly allocated slab */ - slab->frozen = 1; defer_deactivate_slab(slab, NULL); return NULL; } @@ -6471,9 +6470,12 @@ static void free_deferred_objects(struct irq_work *work) struct slab *slab = container_of(pos, struct slab, llnode); #ifdef CONFIG_SLUB_TINY - discard_slab(slab->slab_cache, slab); + free_slab(slab->slab_cache, slab); #else - deactivate_slab(slab->slab_cache, slab, slab->flush_freelist); + if (slab->frozen) + deactivate_slab(slab->slab_cache, slab, slab->flush_freelist); + else + free_slab(slab->slab_cache, slab); #endif } }