Re: xfs resize: primary superblock is not updated immediately

[Dave Chinner <david@fromorbit.com>]

On Tue, Mar 01, 2016 at 08:16:28AM +1100, Dave Chinner wrote:
> On Mon, Feb 29, 2016 at 11:47:54AM +0200, Alex Lyakas wrote:
> Which means it's through the first phase of log recovery and it's
> not failing in log recovery. i.e. we are now running
> xfs_initialize_perag_data() after log recovery. So, as I said a
> couple of posts back up this thread:
> 
> | If log recovery succeeds, then yes, I can see that there is a
> | problem here because the per-ag tree is not reinitialised after
> | the superblock is re-read. That's a pretty easy fix, though (3-4
> | lines of code in xlog_do_recover() to detect a change in
> | filesystem block count and call xfs_initialize_perag() again..

Patch below.

-- 
Dave Chinner
david@fromorbit.com


xfs: reinitialise per-AG structures if geometry changes during recovery

From: Dave Chinner <dchinner@redhat.com>

If a crash occurs immediately after a filesystem grow operation, the
updated superblock geometry is found only in the log. After we
recover the log, the superblock is reread and re-initialised and so
has the new geometry in memory. If the new geometry has more AGs
than prior to the grow operation, then the new AGs will not have
in-memory xfs_perag structurea associated with them.

This will result in an oops when the first metadata buffer from a
new AG is looked up in the buffer cache, as the block lies within
the new geometry but then fails to find a perag structure on lookup.
This is easily fixed by simply re-initialising the perag structure
after re-reading the superblock at the conclusion of the first pahse
of log recovery.

This, however, does not fix the case of log recovery requiring
access to metadata in the newly grown space. Fortunately for us,
because the in-core superblock has not been updated, this will
result in detection of access beyond the end of the filesystem
and so recovery will fail at that point. If this proves to be
a problem, then we can address it separately to the current
reported issue.

Reported-by: Alex Lyakas <alex@zadarastorage.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_log_recover.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 1dc0e14..520471b 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -4898,6 +4898,7 @@ xlog_do_recover(
 	xfs_daddr_t	head_blk,
 	xfs_daddr_t	tail_blk)
 {
+	struct xfs_mount *mp = log->l_mp;
 	int		error;
 	xfs_buf_t	*bp;
 	xfs_sb_t	*sbp;
@@ -4912,7 +4913,7 @@ xlog_do_recover(
 	/*
 	 * If IO errors happened during recovery, bail out.
 	 */
-	if (XFS_FORCED_SHUTDOWN(log->l_mp)) {
+	if (XFS_FORCED_SHUTDOWN(mp)) {
 		return -EIO;
 	}
 
@@ -4925,13 +4926,13 @@ xlog_do_recover(
 	 * or iunlinks they will have some entries in the AIL; so we look at
 	 * the AIL to determine how to set the tail_lsn.
 	 */
-	xlog_assign_tail_lsn(log->l_mp);
+	xlog_assign_tail_lsn(mp);
 
 	/*
 	 * Now that we've finished replaying all buffer and inode
 	 * updates, re-read in the superblock and reverify it.
 	 */
-	bp = xfs_getsb(log->l_mp, 0);
+	bp = xfs_getsb(mp, 0);
 	bp->b_flags &= ~(XBF_DONE | XBF_ASYNC);
 	ASSERT(!(bp->b_flags & XBF_WRITE));
 	bp->b_flags |= XBF_READ;
@@ -4939,7 +4940,7 @@ xlog_do_recover(
 
 	error = xfs_buf_submit_wait(bp);
 	if (error) {
-		if (!XFS_FORCED_SHUTDOWN(log->l_mp)) {
+		if (!XFS_FORCED_SHUTDOWN(mp)) {
 			xfs_buf_ioerror_alert(bp, __func__);
 			ASSERT(0);
 		}
@@ -4948,14 +4949,17 @@ xlog_do_recover(
 	}
 
 	/* Convert superblock from on-disk format */
-	sbp = &log->l_mp->m_sb;
+	sbp = &mp->m_sb;
 	xfs_sb_from_disk(sbp, XFS_BUF_TO_SBP(bp));
-	ASSERT(sbp->sb_magicnum == XFS_SB_MAGIC);
-	ASSERT(xfs_sb_good_version(sbp));
-	xfs_reinit_percpu_counters(log->l_mp);
-
 	xfs_buf_relse(bp);
 
+	/* re-initialise in-core superblock and geometry structures */
+	xfs_reinit_percpu_counters(mp);
+	error = xfs_initialize_perag(mp, sbp->sb_agcount, &mp->m_maxagi);
+	if (error) {
+		xfs_warn(mp, "Failed post-recovery per-ag init: %d", error);
+		return error;
+	}
 
 	xlog_recover_check_summary(log);
 

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