[PATCH] 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.
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 --- 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;
/*
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@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
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 size;
/* this might be an aliased kmem_cache */
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;
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;
/*
On Mon, Nov 04, 2024 at 04:40:12PM +0100, Vlastimil Babka wrote:
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@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
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?
Yeah, I was thinking similar stuff -- the aligned stuff is the alias for the actual stuff.
I like the bitmask for tracking the aliases. :)
On Tue, Nov 05, 2024 at 12:08:37AM +0900, 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:
Wouldn't this be easier?
+++ b/arch/arm64/include/asm/cache.h @@ -33,7 +33,11 @@ * the CPU. */ #define ARCH_DMA_MINALIGN (128) +#ifdef CONFIG_KASAN_HW_TAGS +#define ARCH_KMALLOC_MINALIGN (16) +#else #define ARCH_KMALLOC_MINALIGN (8) +#endif
#ifndef __ASSEMBLY__
On 11/4/24 19:00, Matthew Wilcox wrote:
On Tue, Nov 05, 2024 at 12:08:37AM +0900, 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:
Wouldn't this be easier?
They wanted it to depend on actual HW capability / kernel parameter, see d949a8155d13 ("mm: make minimum slab alignment a runtime property")
Also Catalin's commit referenced above was part of the series that made the alignment more dynamic for other cases IIRC. So I doubt we can simply reduce it back to a build-time constant.
+++ b/arch/arm64/include/asm/cache.h @@ -33,7 +33,11 @@
- the CPU.
*/ #define ARCH_DMA_MINALIGN (128) +#ifdef CONFIG_KASAN_HW_TAGS +#define ARCH_KMALLOC_MINALIGN (16) +#else #define ARCH_KMALLOC_MINALIGN (8) +#endif
#ifndef __ASSEMBLY__
On Mon, Nov 04, 2024 at 07:16:20PM +0100, Vlastimil Babka wrote:
On 11/4/24 19:00, Matthew Wilcox wrote:
On Tue, Nov 05, 2024 at 12:08:37AM +0900, 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:
Wouldn't this be easier?
They wanted it to depend on actual HW capability / kernel parameter, see d949a8155d13 ("mm: make minimum slab alignment a runtime property")
Also Catalin's commit referenced above was part of the series that made the alignment more dynamic for other cases IIRC. So I doubt we can simply reduce it back to a build-time constant.
I principle, I wouldn't reduce it back to constant though the 8 vs 16 difference is not significant. It matter if one enables KASAN_HW_TAGS and wants to run it on hardware without MTE, getting the *-8 caches back.
That said, I haven't managed to trigger this warning yet. Do I need other config options than KASAN_HW_TAGS and DEBUG_VM?
On Mon, Nov 04, 2024 at 10:22:37PM +0000, Catalin Marinas wrote:
On Mon, Nov 04, 2024 at 07:16:20PM +0100, Vlastimil Babka wrote:
On 11/4/24 19:00, Matthew Wilcox wrote:
On Tue, Nov 05, 2024 at 12:08:37AM +0900, 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:
Wouldn't this be easier?
They wanted it to depend on actual HW capability / kernel parameter, see d949a8155d13 ("mm: make minimum slab alignment a runtime property")
Also Catalin's commit referenced above was part of the series that made the alignment more dynamic for other cases IIRC. So I doubt we can simply reduce it back to a build-time constant.
I principle, I wouldn't reduce it back to constant though the 8 vs 16 difference is not significant. It matter if one enables KASAN_HW_TAGS and wants to run it on hardware without MTE, getting the *-8 caches back.
That said, I haven't managed to trigger this warning yet. Do I need other config options than KASAN_HW_TAGS and DEBUG_VM?
Ah, I was missing SLAB_BUCKETS. I'll have a look tomorrow.
linux-stable-mirror@lists.linaro.org
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Catalin Marinas -
Kees Cook -
Koichiro Den -
Matthew Wilcox -
Vlastimil Babka