linux-ext4 - Re: [PATCH 3/4] jbd2: restart replay without revokes if journal block csum fails

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Date:	Thu, 11 Sep 2014 15:15:11 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/4] jbd2: restart replay without revokes if journal
 block csum fails

On Wed 10-09-14 17:28:38, Darrick J. Wong wrote:
> If, during a journal_checksum_v3 replay we encounter a block that
> doesn't match its tag in the descriptor block tag, we need to restart
> the replay without the revoke table in the hopes of replaying the
> newest non-corrupt version of the block that we possibly can.
  Ho hum, I don't like this. If you just ignore revoke list, you'll happily
overwrite freshly allocated data blocks with older metadata. Also when
verifying the checksum, we already know the block hasn't been revoked
so what's even the benefit of ignoring the revoke list?

								Honza
 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  fs/jbd2/recovery.c |   19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index 9b329b5..0094d8b 100644
> --- a/fs/jbd2/recovery.c
> +++ b/fs/jbd2/recovery.c
> @@ -439,6 +439,7 @@ static int do_one_pass(journal_t *journal,
>  	 * block offsets): query the superblock.
>  	 */
>  
> +restart_pass:
>  	sb = journal->j_superblock;
>  	next_commit_ID = be32_to_cpu(sb->s_sequence);
>  	next_log_block = be32_to_cpu(sb->s_start);
> @@ -585,7 +586,8 @@ static int do_one_pass(journal_t *journal,
>  					/* If the block has been
>  					 * revoked, then we're all done
>  					 * here. */
> -					if (jbd2_journal_test_revoke
> +					if (!block_error &&
> +					    jbd2_journal_test_revoke
>  					    (journal, blocknr,
>  					     next_commit_ID)) {
>  						brelse(obh);
> @@ -599,11 +601,24 @@ static int do_one_pass(journal_t *journal,
>  						be32_to_cpu(tmp->h_sequence))) {
>  						brelse(obh);
>  						success = -EIO;
> +						if (!block_error) {
> +							/* If we see a corrupt
> +							 * block, kill the
> +							 * revoke list and
> +							 * restart the replay
> +							 * so that the blocks
> +							 * are as close to
> +							 * accurate as
> +							 * possible. */
> +							jbd2_journal_clear_revoke(journal);
> +							brelse(bh);
> +							block_error = 1;
> +							goto restart_pass;
> +						}
>  						printk(KERN_ERR "JBD2: Invalid "
>  						       "checksum recovering "
>  						       "block %llu in log\n",
>  						       blocknr);
> -						block_error = 1;
>  						goto skip_write;
>  					}
>  
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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