linux-ext4 - Re: [PATCH v3] jbd2: Fix potential data lost in recovering journal raced with synchronizing fs bdev

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Date:   Tue, 19 Sep 2023 12:14:38 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhihao Cheng <chengzhihao1@...wei.com>
Cc:     tytso@....edu, jack@...e.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH v3] jbd2: Fix potential data lost in recovering journal
 raced with synchronizing fs bdev

On Tue 19-09-23 09:25:25, Zhihao Cheng wrote:
> JBD2 makes sure journal data is fallen on fs device by sync_blockdev(),
> however, other process could intercept the EIO information from bdev's
> mapping, which leads journal recovering successful even EIO occurs during
> data written back to fs device.
> 
> We found this problem in our product, iscsi + multipath is chosen for block
> device of ext4. Unstable network may trigger kpartx to rescan partitions in
> device mapper layer. Detailed process is shown as following:
> 
>   mount          kpartx          irq
> jbd2_journal_recover
>  do_one_pass
>   memcpy(nbh->b_data, obh->b_data) // copy data to fs dev from journal
>   mark_buffer_dirty // mark bh dirty
>          vfs_read
> 	  generic_file_read_iter // dio
> 	   filemap_write_and_wait_range
> 	    __filemap_fdatawrite_range
> 	     do_writepages
> 	      block_write_full_folio
> 	       submit_bh_wbc
> 	            >>  EIO occurs in disk  <<
> 	                     end_buffer_async_write
> 			      mark_buffer_write_io_error
> 			       mapping_set_error
> 			        set_bit(AS_EIO, &mapping->flags) // set!
> 	    filemap_check_errors
> 	     test_and_clear_bit(AS_EIO, &mapping->flags) // clear!
>  err2 = sync_blockdev
>   filemap_write_and_wait
>    filemap_check_errors
>     test_and_clear_bit(AS_EIO, &mapping->flags) // false
>  err2 = 0
> 
> Filesystem is mounted successfully even data from journal is failed written
> into disk, and ext4/ocfs2 could become corrupted.
> 
> Fix it by comparing the wb_err state in fs block device before recovering
> and after recovering.
> 
> Fetch a reproducer in [Link].
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217888
> Cc: stable@...r.kernel.org
> Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> ---
>  v1->v3: Initialize wb_err. Untialized wb_err could be same with
> 	 mapping->wb_err(eg. EIO without ERRSEQ_SEEN). When EIO
> 	 occurs again, mapping->wb_err won't be changed, and wb_err
> 	 is still same with mapping->wb_err.

Yeah, good catch. The patch still looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza


>  fs/jbd2/recovery.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index c269a7d29a46..5b771a3d8d9a 100644
> --- a/fs/jbd2/recovery.c
> +++ b/fs/jbd2/recovery.c
> @@ -289,6 +289,8 @@ int jbd2_journal_recover(journal_t *journal)
>  	journal_superblock_t *	sb;
>  
>  	struct recovery_info	info;
> +	errseq_t		wb_err;
> +	struct address_space	*mapping;
>  
>  	memset(&info, 0, sizeof(info));
>  	sb = journal->j_superblock;
> @@ -306,6 +308,9 @@ int jbd2_journal_recover(journal_t *journal)
>  		return 0;
>  	}
>  
> +	wb_err = 0;
> +	mapping = journal->j_fs_dev->bd_inode->i_mapping;
> +	errseq_check_and_advance(&mapping->wb_err, &wb_err);
>  	err = do_one_pass(journal, &info, PASS_SCAN);
>  	if (!err)
>  		err = do_one_pass(journal, &info, PASS_REVOKE);
> @@ -327,6 +332,9 @@ int jbd2_journal_recover(journal_t *journal)
>  
>  	jbd2_journal_clear_revoke(journal);
>  	err2 = sync_blockdev(journal->j_fs_dev);
> +	if (!err)
> +		err = err2;
> +	err2 = errseq_check_and_advance(&mapping->wb_err, &wb_err);
>  	if (!err)
>  		err = err2;
>  	/* Make sure all replayed data is on permanent storage */
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR