From d3c58f24be1bf10fa9e11977080a2398ddcd8361 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 6 Aug 2020 23:19:01 -0700 Subject: mm, slab/slub: move and improve cache_from_obj() 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-guro@fb.com Signed-off-by: Vlastimil Babka Signed-off-by: Andrew Morton Cc: Christoph Lameter Cc: Jann Horn Cc: Kees Cook Cc: Vijayanand Jitta Cc: David Rientjes Cc: Joonsoo Kim Cc: Pekka Enberg Link: http://lkml.kernel.org/r/20200610163135.17364-10-vbabka@suse.cz Signed-off-by: Linus Torvalds --- mm/slub.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index 0b80a8409836..6a99a3c945cb 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1525,6 +1525,10 @@ 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 */ /* @@ -3171,6 +3175,23 @@ 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); -- cgit v1.2.3