Commit b035f5a6d852 ("mm: slab: reduce the kmalloc() minimum alignment if DMA bouncing possible") reduced ARCH_KMALLOC_MINALIGN to 8 on arm64. However, with KASAN_HW_TAGS enabled, arch_slab_minalign() becomes 16. This causes kmalloc_caches[*][8] to be aliased to kmalloc_caches[*][16], resulting in kmem_buckets_create() attempting to create a kmem_cache for size 16 twice. This duplication triggers warnings on boot:

[ 2.325108] ------------[ cut here ]------------ [ 2.325135] kmem_cache of name 'memdup_user-16' already exists [ 2.325783] WARNING: CPU: 0 PID: 1 at mm/slab_common.c:107 __kmem_cache_create_args+0xb8/0x3b0 [ 2.327957] Modules linked in: [ 2.328550] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.0-rc5mm-unstable-arm64+ #12 [ 2.328683] Hardware name: QEMU QEMU Virtual Machine, BIOS 2024.02-2 03/11/2024 [ 2.328790] pstate: 61000009 (nZCv daif -PAN -UAO -TCO +DIT -SSBS BTYPE=--) [ 2.328911] pc : __kmem_cache_create_args+0xb8/0x3b0 [ 2.328930] lr : __kmem_cache_create_args+0xb8/0x3b0 [ 2.328942] sp : ffff800083d6fc50 [ 2.328961] x29: ffff800083d6fc50 x28: f2ff0000c1674410 x27: ffff8000820b0598 [ 2.329061] x26: 000000007fffffff x25: 0000000000000010 x24: 0000000000002000 [ 2.329101] x23: ffff800083d6fce8 x22: ffff8000832222e8 x21: ffff800083222388 [ 2.329118] x20: f2ff0000c1674410 x19: f5ff0000c16364c0 x18: ffff800083d80030 [ 2.329135] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 [ 2.329152] x14: 0000000000000000 x13: 0a73747369786520 x12: 79646165726c6120 [ 2.329169] x11: 656820747563205b x10: 2d2d2d2d2d2d2d2d x9 : 0000000000000000 [ 2.329194] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 [ 2.329210] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 [ 2.329226] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000 [ 2.329291] Call trace: [ 2.329407] __kmem_cache_create_args+0xb8/0x3b0 [ 2.329499] kmem_buckets_create+0xfc/0x320 [ 2.329526] init_user_buckets+0x34/0x78 [ 2.329540] do_one_initcall+0x64/0x3c8 [ 2.329550] kernel_init_freeable+0x26c/0x578 [ 2.329562] kernel_init+0x3c/0x258 [ 2.329574] ret_from_fork+0x10/0x20 [ 2.329698] ---[ end trace 0000000000000000 ]---

[ 2.403704] ------------[ cut here ]------------ [ 2.404716] kmem_cache of name 'msg_msg-16' already exists [ 2.404801] WARNING: CPU: 2 PID: 1 at mm/slab_common.c:107 __kmem_cache_create_args+0xb8/0x3b0 [ 2.404842] Modules linked in: [ 2.404971] CPU: 2 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.12.0-rc5mm-unstable-arm64+ #12 [ 2.405026] Tainted: [W]=WARN [ 2.405043] Hardware name: QEMU QEMU Virtual Machine, BIOS 2024.02-2 03/11/2024 [ 2.405057] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 2.405079] pc : __kmem_cache_create_args+0xb8/0x3b0 [ 2.405100] lr : __kmem_cache_create_args+0xb8/0x3b0 [ 2.405111] sp : ffff800083d6fc50 [ 2.405115] x29: ffff800083d6fc50 x28: fbff0000c1674410 x27: ffff8000820b0598 [ 2.405135] x26: 000000000000ffd0 x25: 0000000000000010 x24: 0000000000006000 [ 2.405153] x23: ffff800083d6fce8 x22: ffff8000832222e8 x21: ffff800083222388 [ 2.405169] x20: fbff0000c1674410 x19: fdff0000c163d6c0 x18: ffff800083d80030 [ 2.405185] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 [ 2.405201] x14: 0000000000000000 x13: 0a73747369786520 x12: 79646165726c6120 [ 2.405217] x11: 656820747563205b x10: 2d2d2d2d2d2d2d2d x9 : 0000000000000000 [ 2.405233] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 [ 2.405248] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 [ 2.405271] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000 [ 2.405287] Call trace: [ 2.405293] __kmem_cache_create_args+0xb8/0x3b0 [ 2.405305] kmem_buckets_create+0xfc/0x320 [ 2.405315] init_msg_buckets+0x34/0x78 [ 2.405326] do_one_initcall+0x64/0x3c8 [ 2.405337] kernel_init_freeable+0x26c/0x578 [ 2.405348] kernel_init+0x3c/0x258 [ 2.405360] ret_from_fork+0x10/0x20 [ 2.405370] ---[ end trace 0000000000000000 ]---

To address this, alias kmem_cache for sizes smaller than min alignment to the aligned sized kmem_cache, as done with the default system kmalloc bucket.

Cc: stable@vger.kernel.org # 6.11.x Fixes: b32801d1255b ("mm/slab: Introduce kmem_buckets_create() and family") Signed-off-by: Koichiro Den koichiro.den@gmail.com --- Changes in v2: - Simplify by just reusing calculated aligned size stored in the default kmalloc_caches --- mm/slab_common.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c index 3d26c257ed8b..db6ffe53c23e 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -380,8 +380,11 @@ kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags, unsigned int usersize, void (*ctor)(void *)) { + unsigned long mask = 0; + unsigned int idx; kmem_buckets *b; - int idx; + + BUILD_BUG_ON(ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]) > BITS_PER_LONG);

/* * When the separate buckets API is not built in, just return @@ -403,7 +406,7 @@ kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags, for (idx = 0; idx < ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]); idx++) { char *short_size, *cache_name; unsigned int cache_useroffset, cache_usersize; - unsigned int size; + unsigned int size, aligned_idx;

if (!kmalloc_caches[KMALLOC_NORMAL][idx]) continue; @@ -416,10 +419,6 @@ kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags, if (WARN_ON(!short_size)) goto fail;

- cache_name = kasprintf(GFP_KERNEL, "%s-%s", name, short_size + 1); - if (WARN_ON(!cache_name)) - goto fail; - if (useroffset >= size) { cache_useroffset = 0; cache_usersize = 0; @@ -427,18 +426,29 @@ kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags, cache_useroffset = useroffset; cache_usersize = min(size - cache_useroffset, usersize); } - (*b)[idx] = kmem_cache_create_usercopy(cache_name, size, - 0, flags, cache_useroffset, - cache_usersize, ctor); - kfree(cache_name); - if (WARN_ON(!(*b)[idx])) - goto fail; + + aligned_idx = __kmalloc_index(size, false); + if (!(*b)[aligned_idx]) { + cache_name = kasprintf(GFP_KERNEL, "%s-%s", name, short_size + 1); + if (WARN_ON(!cache_name)) + goto fail; + (*b)[aligned_idx] = kmem_cache_create_usercopy(cache_name, size, + 0, flags, cache_useroffset, + cache_usersize, ctor); + if (WARN_ON(!(*b)[aligned_idx])) { + kfree(cache_name); + goto fail; + } + set_bit(aligned_idx, &mask); + } + if (idx != aligned_idx) + (*b)[idx] = (*b)[aligned_idx]; }

return b;

fail: - for (idx = 0; idx < ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]); idx++) + for_each_set_bit(idx, &mask, ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL])) kmem_cache_destroy((*b)[idx]); kmem_cache_free(kmem_buckets_cache, b);