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Message-ID: <6125f047-7326-49f7-a568-9cabf80f51c7@suse.cz>
Date: Tue, 5 Nov 2024 17:48:56 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Koichiro Den <koichiro.den@...il.com>,
Catalin Marinas <Catalin.Marinas@....com>
Cc: cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
iamjoonsoo.kim@....com, akpm@...ux-foundation.org, roman.gushchin@...ux.dev,
42.hyeyoo@...il.com, kees@...nel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] mm/slab: fix warning caused by duplicate kmem_cache
creation in kmem_buckets_create
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@...r.kernel.org> # 6.11.x
> Fixes: b32801d1255b ("mm/slab: Introduce kmem_buckets_create() and family")
> Signed-off-by: Koichiro Den <koichiro.den@...il.com>
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
> + 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);
>
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