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Date:   Wed, 29 Jun 2022 12:21:03 +0200
From:   Jan Kara <jack@suse.cz>
To:     Zhang Yi <yi.zhang@huawei.com>
Cc:     linux-ext4@vger.kernel.org, tytso@mit.edu,
        adilger.kernel@dilger.ca, jack@suse.cz, yukuai3@huawei.com
Subject: Re: [PATCH v2 2/2] ext4: check and assert if marking an no_delete
 evicting inode dirty
Message-ID: <20220629102103.y3nmymc26m6qp4jj@quack3>
References: <20220629022940.2855538-1-yi.zhang@huawei.com>
 <20220629022940.2855538-2-yi.zhang@huawei.com>
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On Wed 29-06-22 10:29:40, Zhang Yi wrote:
> In ext4_evict_inode(), if we evicting an inode in the 'no_delete' path,
> it cannot be raced by another mark_inode_dirty(). If it happens,
> someone else may accidentally dirty it without holding inode refcount
> and probably cause use-after-free issues in the writeback procedure.
> It's indiscoverable and hard to debug, so add an ASSERT to check and
> detect this issue in advance.
> 
> Suggested-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
> ---
>  fs/ext4/inode.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 702cc208689a..2ba74412aa89 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -333,6 +333,12 @@ void ext4_evict_inode(struct inode *inode)
>  	ext4_xattr_inode_array_free(ea_inode_array);
>  	return;
>  no_delete:
> +	/*
> +	 * Check out some where else accidentally dirty the evicting inode,
> +	 * which may probably cause inode use-after-free issues later.
> +	 */
> +	ASSERT(list_empty_careful(&inode->i_io_list));

ASSERT() is harsh as it will take the kernel down. Just use WARN_ON_ONCE()
to notify us of the coming problems :).

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR