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Message-ID: <20140912161554.GC5958@quack.suse.cz>
Date: Fri, 12 Sep 2014 18:15:54 +0200
From: Jan Kara <jack@...e.cz>
To: TR Reardon <thomas_reardon@...mail.com>
Cc: Jan Kara <jack@...e.cz>,
"Darrick J. Wong" <darrick.wong@...cle.com>, tytso@....edu,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/4] jbd2: restart replay without revokes if journal
block csum fails
On Fri 12-09-14 09:14:31, TR Reardon wrote:
> Trying to follow your description below, but still have some confusion.
>
> In the most common mount case of metadata-only journalling (no data
> journalling), revokes are emitted when extent blocks or directory blocks
> are released and reused as data blocks? ie updating a metadata block
Yes.
> in-place will never yield a revoke transaction (inodes, bitmaps etc)?
Yes.
Honza
>
> --- Original Message ---
>
> From: "Jan Kara" <jack@...e.cz>
> Sent: September 12, 2014 5:59 AM
> To: "Darrick J. Wong" <darrick.wong@...cle.com>
> Cc: "Jan Kara" <jack@...e.cz>, tytso@....edu, linux-ext4@...r.kernel.org
> Subject: Re: [PATCH 3/4] jbd2: restart replay without revokes if journal block csum fails
>
> On Thu 11-09-14 10:43:29, Darrick J. Wong wrote:
> > On Thu, Sep 11, 2014 at 10:30:09AM -0700, Darrick J. Wong wrote:
> > > On Thu, Sep 11, 2014 at 03:15:11PM +0200, Jan Kara wrote:
> > > > 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 verifying the checksum, we already know the block hasn't been revoked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?
> > >
> > > Let's say block X contains contents B0 and the journal contains:
> > >
> > > 1. write block 1 with B1
> > > 2. revoke "write of block 1 (with B1)"
> > > 3. write block 1 with B2
> > >
> > > Now say that B2 gets corrupt, which means that #3 won't get replayed. Because
> > > the revoke in #2 prevented the write in #1 from being written, at the end of
> > > replay, block 1 has contents B0, even though B1 could have been played back.
> > >
> > > What I'm really confused about is the intent of revoke records -- do they exist
> > > to say "don't replay older versions of this block; a new one will follow
> > > later"? Or they mean only "don't replay this block if it exists in an earlier
> > > transaction" either because a newer block will follow OR because that block is
> > > now something non-journalled (i.e. file data)? I started off thinking the
> > > first, but perhaps it's really the second.
> >
> > Ahh, I get it. Revoke records are used only to indicate that a particular
> > block that's in the journal has become an un-journalled block; a subsequent
> Yup, exactly.
>
> > re-add to the journal removes the revoke record.
> Well, not quite. Block is revoked in some transaction (and that
> information is stored in that transaction in the journal). Thus we don't
> replay that block in older transactions. If in your example B2 gets
> corrupt, replaying B1 has no sense because the existence of revoke record
> means that the block has been reused for data. So metadata in B1 is
> hopelessly outdated anyway.
>
> Honza
>
> > > Rather than dumping the entire revoke list, I think I can just erase the
> > > previous revoke records for just the corrupt block and then restart the replay.
> > >
> > > --D
> > >
> > > >
> > > > 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;
> > > > > }
> > > > >
> > > > >
> > > > > --
> > > > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > > > > the body of a message to majordomo@...r.kernel.org
> > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > > > --
> > > > Jan Kara <jack@...e.cz>
> > > > SUSE Labs, CR
> > > > --
> > > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > > > the body of a message to majordomo@...r.kernel.org
> > > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > > the body of a message to majordomo@...r.kernel.org
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> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
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--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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