mm/slab: fix warning caused by duplicate kmem_cache creation in kmem_buckets_create

mm/slab: fix warning caused by duplicate kmem_cache creation in kmem_buckets_create

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.

Fixes: b32801d1255b ("mm/slab: Introduce kmem_buckets_create() and family")
Cc: <stable@vger.kernel.org> # v6.11+
Signed-off-by: Koichiro Den <koichiro.den@gmail.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>