On Tue, Nov 05, 2024 at 05:48:56PM +0100, Vlastimil Babka wrote:
> On 11/5/24 03:27, Koichiro Den wrote:
> > 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@xxxxxxxxxxxxxxx> # 6.11.x
> > Fixes: b32801d1255b ("mm/slab: Introduce kmem_buckets_create() and family")
> > Signed-off-by: Koichiro Den <koichiro.den@xxxxxxxxx>
>
> Thanks. Given this warning was introduced in 6.12, I'm adding it to the
> slab/for-6.12-rc7/fixes branch so we fix it before 6.12 is final.
>
> > @@ -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);
>
> Note we need to free cache_name always, because kmem_cache_create() does a
> kstrdup_const(), so your change would be creating a memory leak. I've fixed
> it up locally.
>
> Vlastimil
Ugh, sorry about that. Thanks.
>
> > + 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);
> >
>
