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Message-ID: <f72deca7-4344-4adc-88e3-35a4a1d9a30b@suse.cz>
Date: Fri, 3 Oct 2025 09:49:57 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: ranxiaokai627@....com, 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
Subject: Re: [PATCH] slab: Fix using this_cpu_ptr() in preemptible context
On 9/30/25 10:34, ranxiaokai627@....com wrote:
> 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>
Since the slab PR was merged, we should fix this ideally before rc1 so I
updated the code myself per the discussion and added to slab/for-next
Thanks!
----8<----
>From d6306a3d5577769b179ae4e448fd144e2b0f7717 Mon Sep 17 00:00:00 2001
From: Ran Xiaokai <ran.xiaokai@....com.cn>
Date: Tue, 30 Sep 2025 08:34:02 +0000
Subject: [PATCH] slab: Fix using this_cpu_ptr() in preemptible context
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>
Disable preemption in defer_free() and also defer_deactivate_slab() to
make it safe.
[vbabka@...e.cz: disable preemption instead of using raw_cpu_ptr() per
the discussion ]
Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
Link: https://lore.kernel.org/r/20250930083402.782927-1-ranxiaokai627@163.com
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
mm/slub.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 1433f5b988f7..44aa0e3f48ee 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6432,17 +6432,24 @@ 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;
+ guard(preempt)();
+
+ df = this_cpu_ptr(&defer_free_objects);
if (llist_add(head + s->offset, &df->objects))
irq_work_queue(&df->work);
}
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;
slab->flush_freelist = flush_freelist;
+
+ guard(preempt)();
+
+ df = this_cpu_ptr(&defer_free_objects);
if (llist_add(&slab->llnode, &df->slabs))
irq_work_queue(&df->work);
}
--
2.51.0
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