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Re: Re: [PATCH] [PATCH] Stop periodic syncing if filesystem is already

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Re: [PATCH] [PATCH] Stop periodic syncing if filesystem is already shutdown.
From: Raghavendra D Prabhu <raghu.prabhu13@xxxxxxxxx>
Date: Thu, 10 May 2012 01:37:46 +0530
Cc: xfs@xxxxxxxxxxx
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* On Tue, May 08, 2012 at 09:53:21AM +1000, Dave Chinner <david@xxxxxxxxxxxxx> 
On Mon, May 07, 2012 at 02:44:07PM +0530, raghu.prabhu13@xxxxxxxxx wrote:
From: Raghavendra D Prabhu <rprabhu@xxxxxxxxxxx>

This is to prevent syncing from running ad-infinitum till umount if the disk 
has been forcefully unplugged.

This is to prevent messages like these from being displayed.
 fs/xfs/xfs_sync.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index 205ebcb..7ec412c 100644
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -460,6 +460,12 @@ xfs_sync_worker(
                                        struct xfs_mount, m_sync_work);
        int             error;

+       if (!xfs_fs_writable(mp)) {
+               xfs_err(mp, "Filesystem not writable / already shutdown.");
+               xfs_syncd_stop(mp);
+               return;
+       }

That is going to kill the xfssyncd on read only and frozen
filesystems as well as shutdowns, so this is certainly not correct.
The xfs_sync_worker should continue to run until the filesystem is
unmounted, even if it does nothing when it runs.

Yes, in the next patch I had sent -- http://article.gmane.org/gmane.comp.file-systems.xfs.general/45568 -- I removed xfs_syncd_stop from there and added it under xfs_bwrite. (PS: Adding xfs_syncd_stop in xfs_sync_worker was a very bad decision - it sent few of my kworkers to 'D' state and nearly corrupted that fs)

Indeed, all that is needed in xfs_sync_worker() is this:

-       if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {
+       if (!xfs_fs_writable(mp)) {

and the error message won't appear. It fixes the problem for the
shutdown case, as well as handles frozen and read-only filesystems
I realized from your earlier comment that, calling xfs_syncd_stop under xfs_bwrite won't be good either; so I was thinking of just checking for XFS_FORCED_SHUTDOWN(mp) in xfs_log_force and bailing out if already shutdown.

which should take care of xfs_sync_worker, xfs_flush_worker, xfs_iflush and xfs_unmountfs

    Does this sound good?

                /* dgc: errors ignored here */
                if (mp->m_super->s_frozen == SB_UNFROZEN &&
@@ -551,6 +557,12 @@ xfs_flush_worker(
        struct xfs_mount *mp = container_of(work,
                                        struct xfs_mount, m_flush_work);

+       if (!xfs_fs_writable(mp)) {
+               xfs_err(mp, "Filesystem not writable / already shutdown.");
+               xfs_syncd_stop(mp);
+               return;
+       }
        xfs_sync_data(mp, SYNC_TRYLOCK);
        xfs_sync_data(mp, SYNC_TRYLOCK | SYNC_WAIT);

This is not necessary, either, because xfs_sync_data() has shutdown
checks and xfs_flush_worker() should never be called on a shutdown
Yeah, I realized that (sent a patch after this http://article.gmane.org/gmane.comp.file-systems.xfs.general/45568).


Dave Chinner

Raghavendra Prabhu
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