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 <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Roman 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: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 45 insertions, 0 deletions

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