Re: [PATCH] btrfs: sysfs: restore NOFS context on early return in btrfs_sysfs_add_block_group_type()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/10/15 17:23, guolingxing 写道:
> btrfs_sysfs_add_block_group_type() sets up a NOFS context with
> memalloc_nofs_save() because kobject_add() performs GFP_KERNEL
> allocations deep in its call chain, and the function may be called
> while holding a transaction handle or a lock required for a
> transaction commit, where reclaim could deadlock.
> 
> Every other return path of this function calls memalloc_nofs_restore()
> except the early return taken when another thread has already created
> the kobject for the same raid index (this can happen when restriping).
> Taking that path leaves PF_MEMALLOC_NOFS set on the calling task, so
> all subsequent memory allocations performed by that task remain
> restricted to the NOFS scope, which may lead to unexpected allocation
> failures or deadlocks later on.
> 
> Restore the NOFS context before returning from that path.
> 
> Fixes: 49ea112da0e6 ("btrfs: do not create raid sysfs entries under any locks")
> Cc: stable@vger.kernel.org
> Signed-off-by: guolingxing <guolingxing@tju.edu.cn>

Reviewed-by: Qu Wenruo <wqu@suse.com>

> ---
>   fs/btrfs/sysfs.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index 39cb01ee441a..71b1ec6c0643 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -1857,6 +1857,7 @@ void btrfs_sysfs_add_block_group_type(struct btrfs_block_group *cache)
>   	if (space_info->block_group_kobjs[index]) {
>   		spin_unlock(&space_info->lock);
>   		kobject_put(&rkobj->kobj);
> +		memalloc_nofs_restore(nofs_flag);
>   		return;
>   	} else {
>   		space_info->block_group_kobjs[index] = &rkobj->kobj;