Re: [PATCH 06/11] xfs: don't leave EFIs on AIL on mount failure

Brian Foster
2015-08-07T12:10:31Z

On Fri, Aug 07, 2015 at 12:23:36PM +1000, Dave Chinner wrote:
> On Thu, Aug 06, 2015 at 01:44:27PM -0400, Brian Foster wrote:
> > Log recovery occurs in two phases at mount time. In the first phase,
> > EFIs and EFDs are processed and potentially cancelled out. EFIs without
> > EFD objects are inserted into the AIL for processing and recovery in the
> > second phase. xfs_mountfs() runs various other operations between the
> > phases and is thus subject to failure. If failure occurs after the first
> > phase but before the second, pending EFIs sit on the AIL, pin it and
> > cause the mount to hang.
> >
> > Update the mount sequence to ensure that pending EFIs are cancelled in
> > the event of failure. Add a recovery cancellation mechanism to iterate
> > the AIL and cancel all EFI items when requested. Plumb cancellation
> > support through the log mount finish helper and update xfs_mountfs() to
> > invoke cancellation in the event of failure after recovery has started.
> >
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> > fs/xfs/xfs_log.c | 16 +++++++++++-----
> > fs/xfs/xfs_log.h | 2 +-
> > fs/xfs/xfs_log_priv.h | 2 ++
> > fs/xfs/xfs_log_recover.c | 41 ++++++++++++++++++++++++++++++++++++-----
> > fs/xfs/xfs_mount.c | 35 +++++++++++++++++++++++------------
> > 5 files changed, 73 insertions(+), 23 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> > index 6b5a84a..522286c 100644
> > --- a/fs/xfs/xfs_log.c
> > +++ b/fs/xfs/xfs_log.c
> > @@ -740,19 +740,25 @@ out:
> > * it.
> > */
> > int
> > -xfs_log_mount_finish(xfs_mount_t *mp)
> > +xfs_log_mount_finish(
> > + struct xfs_mount *mp,
> > + bool cancel)
> > {
> > int error = 0;
> >
> > - if (!(mp->m_flags & XFS_MOUNT_NORECOVERY)) {
> > + if (mp->m_flags & XFS_MOUNT_NORECOVERY) {
> > + ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
> > + return 0;
> > + }
> > +
> > + if (cancel) {
> > + error = xlog_recover_cancel(mp->m_log);
> > + } else {
> > error = xlog_recover_finish(mp->m_log);
> > if (!error)
> > xfs_log_work_queue(mp);
> > - } else {
> > - ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
> > }
> >
> > -
> > return error;
> > }
>
> As I mentioned on #xfs, I don't think the error/cancel path needs to
> go through this function. Add a new function xfs_log_mount_cancel(),
> and put the contents of xlog_recover_cancel() inside it, along with
> the log unmount function...
>

Ok.

> (General rule: prefix "xfs_log_....()" is for functions that call
> into the log from outside, passing a struct xfs_mount. prefix
> "xlog_...()" is for internal calls, passing a struct xlog.)
>

Sure, xlog_recover_cancel() was just intended to be consistent with
xlog_recover_finish().

> > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> > index a74ff68..a7ba078 100644
> > --- a/fs/xfs/xfs_log_recover.c
> > +++ b/fs/xfs/xfs_log_recover.c
> > @@ -3823,10 +3823,11 @@ abort_error:
> > */
> > STATIC int
> > xlog_recover_process_efis(
> > - struct xlog *log)
> > + struct xlog *log,
> > + bool cancel)
> > {
> > - xfs_log_item_t *lip;
> > - xfs_efi_log_item_t *efip;
> > + struct xfs_log_item *lip;
> > + struct xfs_efi_log_item *efip;
> > int error = 0;
> > struct xfs_ail_cursor cur;
> > struct xfs_ail *ailp;
> > @@ -3847,10 +3848,24 @@ xlog_recover_process_efis(
> > break;
> > }
> >
> > + efip = (struct xfs_efi_log_item *) lip;
> > +
> > + /*
> > + * A cancel occurs when the mount has failed and we're bailing
> > + * out. Release all pending EFIs so they don't pin the AIL.
> > + */
> > + if (cancel) {
> > + spin_unlock(&ailp->xa_lock);
> > + xfs_efi_release(efip);
> > + spin_lock(&ailp->xa_lock);
> > +
> > + lip = xfs_trans_ail_cursor_next(ailp, &cur);
> > + continue;
> > + }
>
> This might be better to separate into a xlog_recover_cancel_efis()
> function because this is much simpler than the rest of the loop.
> It may be more code, but its simpler to read and understand.
>

That was my first instinct, I just didn't want to duplicate the list
processing and whatnot once I looked at it. I'll see how it looks.

> > +
> > /*
> > * Skip EFIs that we've already processed.
> > */
> > - efip = (xfs_efi_log_item_t *)lip;
> > if (test_bit(XFS_EFI_RECOVERED, &efip->efi_flags)) {
> > lip = xfs_trans_ail_cursor_next(ailp, &cur);
> > continue;
> > @@ -4617,8 +4632,13 @@ xlog_recover_finish(
> > */
> > if (log->l_flags & XLOG_RECOVERY_NEEDED) {
> > int error;
> > - error = xlog_recover_process_efis(log);
> > + error = xlog_recover_process_efis(log, false);
> > if (error) {
> > + /*
> > + * We could still have pending EFIs. Cancel them so we
> > + * don't hang...
> > + */
> > + xlog_recover_process_efis(log, true);
>
> Not actually necessary. We don't clear the XLOG_RECOVERY_NEEDED
> flag, so when the error stack is run in xfs_mountfs(), we will
> call xfs_log_mount_cancel(), it will see the XLOG_RECOVERY_NEEDED
> and run xlog_recover_cancel_efis()....
>

Ok.

> > xfs_alert(log->l_mp, "Failed to recover EFIs");
> > return error;
> > }
> > @@ -4644,6 +4664,17 @@ xlog_recover_finish(
> > return 0;
> > }
> >
> > +int
> > +xlog_recover_cancel(
> > + struct xlog *log)
> > +{
> > + int error = 0;
> > +
> > + if (log->l_flags & XLOG_RECOVERY_NEEDED)
> > + error = xlog_recover_process_efis(log, true);
> > +
> > + return error;
> > +}
>
> void
> xfs_log_mount_cancel(
> struct xfs_mount *mp)
> {
> int error = 0;
>
> if (log->l_flags & XLOG_RECOVERY_NEEDED)
> xlog_recover_cancel_efis(log);
>
> xfs_log_unmount(mp);
> return error;
> }
>
> > @@ -799,7 +800,10 @@ xfs_mountfs(
> > }
> >
> > /*
> > - * log's mount-time initialization. Perform 1st part recovery if needed
> > + * Log's mount-time initialization. The first part of recovery can place
> > + * some items on the AIL, to be handled when recovery is finished. Set
> > + * the cancel flag to ensure that the recovery is cancelled should we
> > + * fail before then.
> > */
> > error = xfs_log_mount(mp, mp->m_logdev_targp,
> > XFS_FSB_TO_DADDR(mp, sbp->sb_logstart),
> > @@ -808,6 +812,7 @@ xfs_mountfs(
> > xfs_warn(mp, "log mount failed");
> > goto out_fail_wait;
> > }
> > + log_mount_cancel = true;
>
> At this point, XLOG_RECOVERY_NEEDED will be set if EFI processing is
> required, so a variable to track this here is not needed.
>

Indeed, I didn't notice how XLOG_RECOVERY_NEEDED was used here. This
seems much cleaner.

> > @@ -910,11 +915,15 @@ xfs_mountfs(
> > }
> >
> > /*
> > - * Finish recovering the file system. This part needed to be
> > - * delayed until after the root and real-time bitmap inodes
> > - * were consistently read in.
> > + * Finish recovering the file system. This part needed to be delayed
> > + * until after the root and real-time bitmap inodes were consistently
> > + * read in.
> > + *
> > + * Reset the cancel flag as the finish cleans up after itself on
> > + * failure.
> > */
> > - error = xfs_log_mount_finish(mp);
> > + log_mount_cancel = false;
> > + error = xfs_log_mount_finish(mp, false);
> > if (error) {
> > xfs_warn(mp, "log mount finish failed");
> > goto out_rtunmount;
>
> xfs_log_mount_finish() will clear the XLOG_RECOVERY_NEEDED. On
> error, we jump into the error stack above the call to
> xfs_log_mount_cancel(), so it will handle the cleanup....
>
> > @@ -956,6 +965,8 @@ xfs_mountfs(
> > out_rele_rip:
> > IRELE(rip);
> > out_log_dealloc:
> > + if (log_mount_cancel)
> > + xfs_log_mount_finish(mp, true);
> > xfs_log_unmount(mp);
>
> And this just becomes a call to xfs_log_mount_cancel().
>
> I hope this is a bit clearer that mud ;)
>

I think I follow.. thanks.

Brian

> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>
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