From e42f174e43e47b623d9dbf814521c4961000c962 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 6 Aug 2020 23:19:05 -0700 Subject: mm, slab/slub: improve error reporting and overhead of cache_from_obj() 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. Thus, export the SLUB print_tracking() function and provide an empty one for SLAB. For SLUB we can also benefit from the static key check in kmem_cache_debug_flags(), but we need to move this function to slab.h and declare the static key there. [1] https://lore.kernel.org/r/20200608230654.828134-18-guro@fb.com [vbabka@suse.cz: avoid bogus WARN()] Link: https://lore.kernel.org/r/20200623090213.GW5535@shao2-debian Link: http://lkml.kernel.org/r/b33e0fa7-cd28-4788-9e54-5927846329ef@suse.cz Signed-off-by: Vlastimil Babka Signed-off-by: Andrew Morton Acked-by: Kees Cook Acked-by: Roman Gushchin Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Matthew Garrett Cc: Jann Horn Cc: Vijayanand Jitta Cc: Vinayak Menon Link: http://lkml.kernel.org/r/afeda7ac-748b-33d8-a905-56b708148ad5@suse.cz Signed-off-by: Linus Torvalds --- mm/slab.h | 45 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) (limited to 'mm/slab.h') diff --git a/mm/slab.h b/mm/slab.h index a21c78eccee7..fceb4341ba91 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -276,6 +276,34 @@ static inline int cache_vmstat_idx(struct kmem_cache *s) NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE; } +#ifdef CONFIG_SLUB_DEBUG +#ifdef CONFIG_SLUB_DEBUG_ON +DECLARE_STATIC_KEY_TRUE(slub_debug_enabled); +#else +DECLARE_STATIC_KEY_FALSE(slub_debug_enabled); +#endif +extern void print_tracking(struct kmem_cache *s, void *object); +#else +static inline void print_tracking(struct kmem_cache *s, void *object) +{ +} +#endif + +/* + * Returns true if any of the specified slub_debug flags is enabled for the + * cache. Use only for flags parsed by setup_slub_debug() as it also enables + * the static key. + */ +static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t flags) +{ +#ifdef CONFIG_SLUB_DEBUG + VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS)); + if (static_branch_unlikely(&slub_debug_enabled)) + return s->flags & flags; +#endif + return false; +} + #ifdef CONFIG_MEMCG_KMEM /* List of all root caches. */ @@ -504,6 +532,23 @@ 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; + + 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; +} + static inline size_t slab_ksize(const struct kmem_cache *s) { #ifndef CONFIG_SLUB -- cgit