kmem_buckets_create() clones kmalloc_caches[KMALLOC_NORMAL]. kmalloc_slab() figures out the kmalloc type the caller asks for, but then ignored it whenever a bucket set was in use, returning a normal cache regardless. This would be a problem if a caller asked for GFP_DMA, __GFP_ACCOUNT, etc. None of the current users do this, so there is problem, but it makes adding new users fragile. For example, skb data[1] needs to handle GFP_DMA (rarely) and __GFP_ACCOUNT (often).
Send those allocations to the general caches instead so nothing breaks and regular allocations remain isolated with the bucket. The kmem_bucket_type enum contains only a single item here, but will be expanded in the next patch. Built and tests pass with ARCH=x86_64 defconfig with GCC 16.2.0, with CONFIG_SLAB_BUCKETS as y and n. Assisted-by: LLM Link: https://lore.kernel.org/all/[email protected]/ [1] Signed-off-by: Kees Cook <[email protected]> --- Cc: Vlastimil Babka <[email protected]> Cc: Harry Yoo <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Hao Li <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: David Rientjes <[email protected]> Cc: Roman Gushchin <[email protected]> Cc: <[email protected]> Cc: Pedro Falcato <[email protected]> Cc: Kuniyuki Iwashima <[email protected]> Cc: <[email protected]> --- include/linux/slab.h | 13 +++++++++++ mm/slab.h | 23 ++++++++++++++++-- lib/tests/slub_kunit.c | 53 ++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 87 insertions(+), 2 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 18a2351f9084..ab9ab3d34847 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -742,6 +742,19 @@ typedef struct kmem_cache * kmem_buckets[KMALLOC_SHIFT_HIGH + 1]; extern kmem_buckets kmalloc_caches[NR_KMALLOC_TYPES]; +/* + * The kmalloc types a bucket set can hold a copy of. This is deliberately not + * enum kmalloc_cache_type: the KMALLOC_PARTITION copies are all "normal" to a + * bucket set, which already separates what they were there to separate, so + * indexing by those would mean up to KMALLOC_PARTITION_CACHES_NR unusable + * rows per set. Allocations of any type not listed here are served by the + * general caches. + */ +enum kmem_bucket_type { + KMEM_BUCKET_NORMAL = 0, + NR_KMEM_BUCKET_TYPES +}; + /* * Define gfp bits that should not be set for KMALLOC_NORMAL. */ diff --git a/mm/slab.h b/mm/slab.h index 8fd6835e4235..7f1bfee83b92 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -421,6 +421,26 @@ static inline unsigned int size_index_elem(unsigned int bytes) return (bytes - 1) / 8; } +/* + * Which set of buckets to use for the given kmalloc_cache_type. If not + * handled by the kmem_buckets, fall back to general caches. + */ +static inline kmem_buckets * +kmalloc_choose_bucket(kmem_buckets *bucket, enum kmalloc_cache_type type) +{ + enum kmem_bucket_type btype; + + if (!bucket) + return &kmalloc_caches[type]; + + if (type <= KMALLOC_PARTITION_END) + btype = KMEM_BUCKET_NORMAL; + else + return &kmalloc_caches[type]; /* No set holds a row for it. */ + + return &bucket[btype]; +} + /* * Find the kmem_cache structure that serves a given size of * allocation @@ -438,8 +458,7 @@ kmalloc_slab(size_t size, kmem_buckets *b, gfp_t flags, kmalloc_token_t token, if (alloc_flags & SLAB_ALLOC_NO_OBJ_EXT) type = KMALLOC_NO_OBJ_EXT; - if (!b) - b = &kmalloc_caches[type]; + b = kmalloc_choose_bucket(b, type); if (size <= 192) index = kmalloc_size_index[size_index_elem(size)]; else diff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c index d6467dd5cf9b..823607e06248 100644 --- a/lib/tests/slub_kunit.c +++ b/lib/tests/slub_kunit.c @@ -683,6 +683,58 @@ static void test_kmem_buckets_destroy(struct kunit *test) KUNIT_EXPECT_EQ(test, 2, slab_errors); } +/* + * A bucket set holds only the kmalloc types it was created with, so an + * allocation that asks for a different one has to come from the general + * caches. Check that it does, rather than being served a normal cache that + * does not satisfy what the flags asked for. + */ +static void test_kmem_buckets_type_fallback(struct kunit *test) +{ + struct kmem_cache *c; + kmem_buckets *b; + void *p; + + if (!IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "needs CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("test_buckets", 0, 0, INT_MAX, NULL); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + /* A plain allocation stays isolated in the bucket set. */ + p = kmem_buckets_alloc(b, 128, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, c); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "test_buckets-"), + "expected a bucket cache, got %s", c->name); + + /* One that needs ZONE_DMA cannot, so it falls back. */ + if (IS_ENABLED(CONFIG_ZONE_DMA)) { + p = kmem_buckets_alloc(b, 128, GFP_KERNEL | GFP_DMA); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, c); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "dma-kmalloc-"), + "expected a DMA cache, got %s", c->name); + } + + /* Nor can one that has to be accounted. */ + if (IS_ENABLED(CONFIG_MEMCG) && !mem_cgroup_kmem_disabled()) { + p = kmem_buckets_alloc(b, 128, GFP_KERNEL | __GFP_ACCOUNT); + KUNIT_ASSERT_NOT_NULL(test, p); + c = virt_to_slab(p)->slab_cache; + kfree(p); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "kmalloc-cg-"), + "expected an accounted cache, got %s", c->name); + } +} + static struct kunit_case test_cases[] = { KUNIT_CASE(test_clobber_zone), @@ -709,6 +761,7 @@ static struct kunit_case test_cases[] = { KUNIT_CASE(test_kmem_buckets_alignment), KUNIT_CASE(test_kmem_buckets_disabled), KUNIT_CASE(test_kmem_buckets_destroy), + KUNIT_CASE(test_kmem_buckets_type_fallback), {} }; -- 2.34.1
