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Message-ID: <20241104150837.2756047-1-koichiro.den@gmail.com>
Date: Tue,  5 Nov 2024 00:08:37 +0900
From: Koichiro Den <koichiro.den@...il.com>
To: vbabka@...e.cz
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,
	koichiro.den@...il.com
Subject: [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@...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>
---
 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;
 
 	/*
-- 
2.43.0


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