Re: [PATCH] slab: Fix using this_cpu_ptr() in preemptible context

Harry Yoo
2025-10-13T07:00:44Z

On Fri, Oct 03, 2025 at 09:49:57AM +0200, Vlastimil Babka wrote:
> On 9/30/25 10:34, ranxiaokai627@163.com wrote:
> > From: Ran Xiaokai <ran.xiaokai@zte.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@zte.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@zte.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@suse.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@zte.com.cn>
> Link: https://lore.kernel.org/r/20250930083402.782927-1-ranxiaokai627@163.com
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---

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

--
Cheers,
Harry / Hyeonggon