linux-ext4 - Re: [PATCH 3/3] ext4: Avoid freeing inodes on dirty list

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Message-ID: <20200514145744.GW1596452@mit.edu>
Date:   Thu, 14 May 2020 10:57:44 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Eric Sandeen <sandeen@...deen.net>
Subject: Re: [PATCH 3/3] ext4: Avoid freeing inodes on dirty list

On Tue, Apr 21, 2020 at 10:54:45AM +0200, Jan Kara wrote:
> When we are evicting inode with journalled data, we may race with
> transaction commit in the following way:
> 
> CPU0					CPU1
> jbd2_journal_commit_transaction()	evict(inode)
> 					  inode_io_list_del()
> 					  inode_wait_for_writeback()
>   process BJ_Forget list
>     __jbd2_journal_insert_checkpoint()
>     __jbd2_journal_refile_buffer()
>       __jbd2_journal_unfile_buffer()
>         if (test_clear_buffer_jbddirty(bh))
>           mark_buffer_dirty(bh)
> 	    __mark_inode_dirty(inode)
> 					  ext4_evict_inode(inode)
> 					    frees the inode
> 
> This results in use-after-free issues in the writeback code (or
> the assertion added in the previous commit triggering).
> 
> Fix the problem by removing inode from writeback lists once all the page
> cache is evicted and so inode cannot be added to writeback lists again.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

Applied, thanks.

						- Ted