linux-kernel - Re: [PATCH v3] shmem: fix a race between shmem_unused_huge_shrink and shmem_evict

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Message-ID: <20211124200618.adaxuxuksrinkigv@box.shutemov.name>
Date:   Wed, 24 Nov 2021 23:06:18 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Gang Li <ligang.bdlg@...edance.com>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        stable@...r.kernel.org, songmuchun@...edance.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] shmem: fix a race between shmem_unused_huge_shrink
 and shmem_evict_inode

On Wed, Nov 24, 2021 at 05:43:16PM +0800, Gang Li wrote:
> +move_back:
> +		/* inodes that are on @list and will not be deleted must be moved back to
> +		 * global list before iput for two reasons:
> +		 * 1. iput in lock: iput call shmem_evict_inode, then cause deadlock.
> +		 * 2. iput before lock: shmem_evict_inode may grab the inode on @list,
> +		 *    which will cause race.
> +		 */
> +		spin_lock(&sbinfo->shrinklist_lock);
> +		list_move(&info->shrinklist, &sbinfo->shrinklist);
> +		sbinfo->shrinklist_len++;
> +		spin_unlock(&sbinfo->shrinklist_lock);
> +put:
>  		iput(inode);
>  	}
>  
> -	spin_lock(&sbinfo->shrinklist_lock);
> -	list_splice_tail(&list, &sbinfo->shrinklist);
> -	sbinfo->shrinklist_len -= removed;
> -	spin_unlock(&sbinfo->shrinklist_lock);
> -
>  	return split;
>  }

Okay, I guess it works. Locking is not pretty, but well..

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov