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

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Message-ID: <aOyjfyCSgoIj_c_H@hyeyoo>
Date: Mon, 13 Oct 2025 16:00:15 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: ranxiaokai627@....com, akpm@...ux-foundation.org, cl@...two.org,
        rientjes@...gle.com, roman.gushchin@...ux.dev, ast@...nel.org,
        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 Fri, Oct 03, 2025 at 09:49:57AM +0200, Vlastimil Babka wrote:
> 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>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>

-- 
Cheers,
Harry / Hyeonggon