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

[Vlastimil Babka]

On 9/30/25 10:34, ranxiaokai627@xxxxxxx wrote:
> From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>

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!

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