The function cache_from_obj() was added by commit b9ce5ef49f00 ("sl[au]b: always get the cache from its page in kmem_cache_free()") to support kmemcg, where per-memcg cache can be different from the root one, so we can't use the kmem_cache pointer given to kmem_cache_free().
Prior to that commit, SLUB already had debugging check+warning that could be enabled to compare the given kmem_cache pointer to one referenced by the slab page where the object-to-be-freed resides. This check was moved to cache_from_obj(). Later the check was also enabled for SLAB_FREELIST_HARDENED configs by commit 598a0717a816 ("mm/slab: validate cache membership under freelist hardening"). These checks and warnings can be useful especially for the debugging, which can be improved. Commit 598a0717a816 changed the pr_err() with WARN_ON_ONCE() to WARN_ONCE() so only the first hit is now reported, others are silent. This patch changes it to WARN() so that all errors are reported. It's also useful to print SLUB allocation/free tracking info for the offending object, if tracking is enabled. We could export the SLUB print_tracking() function and provide an empty one for SLAB, or realize that both the debugging and hardening cases in cache_from_obj() are only supported by SLUB anyway. So this patch moves cache_from_obj() from slab.h to separate instances in slab.c and slub.c, where the SLAB version only does the kmemcg lookup and even could be completely removed once the kmemcg rework [1] is merged. The SLUB version can thus easily use the print_tracking() function. It can also use the kmem_cache_debug_flags() static key check for improved performance in kernels without the hardening and with debugging not enabled on boot. [1] https://lore.kernel.org/r/20200608230654.828134-18-g...@fb.com Signed-off-by: Vlastimil Babka <vba...@suse.cz> --- mm/slab.c | 8 ++++++++ mm/slab.h | 23 ----------------------- mm/slub.c | 21 +++++++++++++++++++++ 3 files changed, 29 insertions(+), 23 deletions(-) diff --git a/mm/slab.c b/mm/slab.c index 9350062ffc1a..6134c4c36d4c 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3672,6 +3672,14 @@ void *__kmalloc_track_caller(size_t size, gfp_t flags, unsigned long caller) } EXPORT_SYMBOL(__kmalloc_track_caller); +static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) +{ + if (memcg_kmem_enabled()) + return virt_to_cache(x); + else + return s; +} + /** * kmem_cache_free - Deallocate an object * @cachep: The cache the allocation was from. diff --git a/mm/slab.h b/mm/slab.h index 815e4e9a94cd..c0c4244f75da 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -503,29 +503,6 @@ static __always_inline void uncharge_slab_page(struct page *page, int order, memcg_uncharge_slab(page, order, s); } -static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) -{ - struct kmem_cache *cachep; - - /* - * When kmemcg is not being used, both assignments should return the - * same value. but we don't want to pay the assignment price in that - * case. If it is not compiled in, the compiler should be smart enough - * to not do even the assignment. In that case, slab_equal_or_root - * will also be a constant. - */ - if (!memcg_kmem_enabled() && - !IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && - !unlikely(s->flags & SLAB_CONSISTENCY_CHECKS)) - return s; - - cachep = virt_to_cache(x); - WARN_ONCE(cachep && !slab_equal_or_root(cachep, s), - "%s: Wrong slab cache. %s but object is from %s\n", - __func__, s->name, cachep->name); - return cachep; -} - static inline size_t slab_ksize(const struct kmem_cache *s) { #ifndef CONFIG_SLUB diff --git a/mm/slub.c b/mm/slub.c index efb08f2e9c66..f7a1d8537674 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1524,6 +1524,10 @@ static bool freelist_corrupted(struct kmem_cache *s, struct page *page, { return false; } + +static void print_tracking(struct kmem_cache *s, void *object) +{ +} #endif /* CONFIG_SLUB_DEBUG */ /* @@ -3175,6 +3179,23 @@ void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr) } #endif +static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) +{ + struct kmem_cache *cachep; + + if (!IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && + !memcg_kmem_enabled() && + !kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) + return s; + + cachep = virt_to_cache(x); + if (WARN(cachep && !slab_equal_or_root(cachep, s), + "%s: Wrong slab cache. %s but object is from %s\n", + __func__, s->name, cachep->name)) + print_tracking(cachep, x); + return cachep; +} + void kmem_cache_free(struct kmem_cache *s, void *x) { s = cache_from_obj(s, x); -- 2.26.2