linux-kernel - [PATCH] slab: Fix using this_cpu

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Message-ID: <20250930083402.782927-1-ranxiaokai627@163.com>
Date: Tue, 30 Sep 2025 08:34:02 +0000
From: ranxiaokai627@....com
To: vbabka@...e.cz,
	akpm@...ux-foundation.org,
	cl@...two.org,
	rientjes@...gle.com,
	roman.gushchin@...ux.dev,
	harry.yoo@...cle.com,
	ast@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	ran.xiaokai@....com.cn,
	ranxiaokai627@....com
Subject: [PATCH] slab: Fix using this_cpu_ptr() in preemptible context

From: Ran Xiaokai <ran.xiaokai@....com.cn>

defer_free() maybe called in preemptible context, this will
trigger the below warning message:

BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
caller is defer_free+0x1b/0x60
Call Trace:
 <TASK>
 dump_stack_lvl+0xac/0xc0
 check_preemption_disabled+0xbe/0xe0
 defer_free+0x1b/0x60
 kfree_nolock+0x1eb/0x2b0
 alloc_slab_obj_exts+0x356/0x390
 __alloc_tagging_slab_alloc_hook+0xa0/0x300
 __kmalloc_cache_noprof+0x1c4/0x5c0
 __set_page_owner+0x10d/0x1c0
 post_alloc_hook+0x84/0xf0
 get_page_from_freelist+0x73b/0x1380
 __alloc_frozen_pages_noprof+0x110/0x2c0
 alloc_pages_mpol+0x44/0x140
 alloc_slab_page+0xac/0x150
 allocate_slab+0x78/0x3a0
 ___slab_alloc+0x76b/0xed0
 __slab_alloc.constprop.0+0x5a/0xb0
 __kmalloc_noprof+0x3dc/0x6d0
 __list_lru_init+0x6c/0x210
 alloc_super+0x3b6/0x470
 sget_fc+0x5f/0x3a0
 get_tree_nodev+0x27/0x90
 vfs_get_tree+0x26/0xc0
 vfs_kern_mount.part.0+0xb6/0x140
 kern_mount+0x24/0x40
 init_pipe_fs+0x4f/0x70
 do_one_initcall+0x62/0x2e0
 kernel_init_freeable+0x25b/0x4b0
 kernel_init+0x1a/0x1c0
 ret_from_fork+0x290/0x2e0
 ret_from_fork_asm+0x11/0x20
</TASK>

Replace this_cpu_ptr with raw_cpu_ptr to eliminate
the above warning message.

Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
---
 mm/slub.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 1433f5b988f7..67c57f1b5a86 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6432,7 +6432,7 @@ static void free_deferred_objects(struct irq_work *work)
 
 static void defer_free(struct kmem_cache *s, void *head)
 {
-	struct defer_free *df = this_cpu_ptr(&defer_free_objects);
+	struct defer_free *df = raw_cpu_ptr(&defer_free_objects);
 
 	if (llist_add(head + s->offset, &df->objects))
 		irq_work_queue(&df->work);
@@ -6440,7 +6440,7 @@ static void defer_free(struct kmem_cache *s, void *head)
 
 static void defer_deactivate_slab(struct slab *slab, void *flush_freelist)
 {
-	struct defer_free *df = this_cpu_ptr(&defer_free_objects);
+	struct defer_free *df = raw_cpu_ptr(&defer_free_objects);
 
 	slab->flush_freelist = flush_freelist;
 	if (llist_add(&slab->llnode, &df->slabs))
-- 
2.25.1