Commit e42f174e authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm, slab/slub: improve error reporting and overhead of cache_from_obj() 

cache_from_obj() was added by commit b9ce5ef4 ("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 598a0717 ("mm/slab: validate
cache membership under freelist hardening").

These checks and warnings can be useful especially for the debugging,
which can be improved.  Commit 598a0717 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: default avatarVlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarRoman Gushchin <guro@fb.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Garrett <mjg59@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Vinayak Menon <vinmenon@codeaurora.org>
Link: http://lkml.kernel.org/r/afeda7ac-748b-33d8-a905-56b708148ad5@suse.cz


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d3c58f24

mm/slab.c

+0 −8
Original line number Diff line number Diff line
@@ -3678,14 +3678,6 @@ 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.

mm/slab.h

+45 −0
Original line number Diff line number Diff line
@@ -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

mm/slub.c

+1 −37
Original line number Diff line number Diff line
@@ -122,21 +122,6 @@ DEFINE_STATIC_KEY_FALSE(slub_debug_enabled); 
#endif

#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)

{

	VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS));

#ifdef CONFIG_SLUB_DEBUG

	if (static_branch_unlikely(&slub_debug_enabled))

		return s->flags & flags;

#endif

	return false;

}



static inline bool kmem_cache_debug(struct kmem_cache *s)

{

	return kmem_cache_debug_flags(s, SLAB_DEBUG_FLAGS);
@@ -653,7 +638,7 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time) 
#endif

}



static void print_tracking(struct kmem_cache *s, void *object)

void print_tracking(struct kmem_cache *s, void *object)

{

	unsigned long pr_time = jiffies;

	if (!(s->flags & SLAB_STORE_USER))
@@ -1525,10 +1510,6 @@ 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 */



/*
@@ -3175,23 +3156,6 @@ 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);

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