On 11/4/24 16:08, 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 for catching this.
Wonder if we could make this a lot simpler in kmem_buckets_create() by
starting with the current:
size = kmalloc_caches[KMALLOC_NORMAL][idx]->object_size;
and adding:
aligned_idx = __kmalloc_index(size, false);
now the rest of the loop iteration would work with aligned_idx and if it
differs from idx, we assign the cache pointer also to idx, etc.
This should avoid duplicating the alignment calculation as we just extract
from kmalloc_caches[] the result of what new_kmalloc_cache() already did?
Vlastimil
> mm/slab_common.c | 102 ++++++++++++++++++++++++++++-------------------
> 1 file changed, 62 insertions(+), 40 deletions(-)
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 3d26c257ed8b..64140561dd0e 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -354,6 +354,38 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
> }
> EXPORT_SYMBOL(__kmem_cache_create_args);
>
> +static unsigned int __kmalloc_minalign(void)
> +{
> + unsigned int minalign = dma_get_cache_alignment();
> +
> + if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
> + is_swiotlb_allocated())
> + minalign = ARCH_KMALLOC_MINALIGN;
> +
> + return max(minalign, arch_slab_minalign());
> +}
> +
> +static unsigned int __kmalloc_aligned_size(unsigned int idx)
> +{
> + unsigned int aligned_size = kmalloc_info[idx].size;
> + unsigned int minalign = __kmalloc_minalign();
> +
> + if (minalign > ARCH_KMALLOC_MINALIGN)
> + aligned_size = ALIGN(aligned_size, minalign);
> +
> + return aligned_size;
> +}
> +
> +static unsigned int __kmalloc_aligned_idx(unsigned int idx)
> +{
> + unsigned int minalign = __kmalloc_minalign();
> +
> + if (minalign > ARCH_KMALLOC_MINALIGN)
> + return __kmalloc_index(__kmalloc_aligned_size(idx), false);
> +
> + return idx;
> +}
> +
> static struct kmem_cache *kmem_buckets_cache __ro_after_init;
>
> /**
> @@ -381,7 +413,10 @@ kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags,
> void (*ctor)(void *))
> {
> kmem_buckets *b;
> - int idx;
> + unsigned int idx;
> + unsigned long mask = 0;
> +
> + BUILD_BUG_ON(ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]) > BITS_PER_LONG);
>
> /*
> * When the separate buckets API is not built in, just return
> @@ -402,43 +437,47 @@ 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 aligned_size = __kmalloc_aligned_size(idx);
> + unsigned int aligned_idx = __kmalloc_aligned_idx(idx);
> unsigned int cache_useroffset, cache_usersize;
> - unsigned int size;
>
> + /* this might be an aliased kmem_cache */
> if (!kmalloc_caches[KMALLOC_NORMAL][idx])
> continue;
>
> - size = kmalloc_caches[KMALLOC_NORMAL][idx]->object_size;
> - if (!size)
> - continue;
> -
> short_size = strchr(kmalloc_caches[KMALLOC_NORMAL][idx]->name, '-');
> 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) {
> + if (useroffset >= aligned_size) {
> cache_useroffset = 0;
> cache_usersize = 0;
> } else {
> cache_useroffset = useroffset;
> - cache_usersize = min(size - cache_useroffset, usersize);
> + cache_usersize = min(aligned_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;
> +
> + 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, aligned_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);
>
> @@ -871,24 +910,12 @@ void __init setup_kmalloc_cache_index_table(void)
> }
> }
>
> -static unsigned int __kmalloc_minalign(void)
> -{
> - unsigned int minalign = dma_get_cache_alignment();
> -
> - if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
> - is_swiotlb_allocated())
> - minalign = ARCH_KMALLOC_MINALIGN;
> -
> - return max(minalign, arch_slab_minalign());
> -}
> -
> static void __init
> -new_kmalloc_cache(int idx, enum kmalloc_cache_type type)
> +new_kmalloc_cache(unsigned int idx, enum kmalloc_cache_type type)
> {
> slab_flags_t flags = 0;
> - unsigned int minalign = __kmalloc_minalign();
> - unsigned int aligned_size = kmalloc_info[idx].size;
> - int aligned_idx = idx;
> + unsigned int aligned_size = __kmalloc_aligned_size(idx);
> + unsigned int aligned_idx = __kmalloc_aligned_idx(idx);
>
> if ((KMALLOC_RECLAIM != KMALLOC_NORMAL) && (type == KMALLOC_RECLAIM)) {
> flags |= SLAB_RECLAIM_ACCOUNT;
> @@ -914,11 +941,6 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type)
> if (IS_ENABLED(CONFIG_MEMCG) && (type == KMALLOC_NORMAL))
> flags |= SLAB_NO_MERGE;
>
> - if (minalign > ARCH_KMALLOC_MINALIGN) {
> - aligned_size = ALIGN(aligned_size, minalign);
> - aligned_idx = __kmalloc_index(aligned_size, false);
> - }
> -
> if (!kmalloc_caches[type][aligned_idx])
> kmalloc_caches[type][aligned_idx] = create_kmalloc_cache(
> kmalloc_info[aligned_idx].name[type],
> @@ -934,7 +956,7 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type)
> */
> void __init create_kmalloc_caches(void)
> {
> - int i;
> + unsigned int i;
> enum kmalloc_cache_type type;
>
> /*
