Post by Mark TinguelyPost by Dave ChinnerPost by Eric SandeenSimilar to xfs_file_fsync(), I think xfs_dir_fsync() needs
to test for a shut down fs, lest we go down paths we'll
never be able to complete; Boris reported that during some
stress tests he had threads stuck in xlog_cil_force_lsn
via xfs_dir_fsync().
[ 3663.361709] sfsuspend-par D ffff88042f0b4540 0 3981 3947 0x00000080
[ 3663.397199] [<ffffffff815f1889>] schedule+0x29/0x70
[ 3663.402743] [<ffffffffa01feda5>] xlog_cil_force_lsn+0x185/0x1a0 [xfs]
[ 3663.416249] [<ffffffffa01fd3af>] _xfs_log_force_lsn+0x6f/0x2f0 [xfs]
[ 3663.429271] [<ffffffffa01a339d>] xfs_dir_fsync+0x7d/0xe0 [xfs]
[ 3663.435873] [<ffffffff811df8c5>] do_fsync+0x65/0xa0
[ 3663.441408] [<ffffffff811dfbc0>] SyS_fsync+0x10/0x20
[ 3663.447043] [<ffffffff815fc7d9>] system_call_fastpath+0x16/0x1b
Wow, I believe it's taken this long for us to notice that we can't
break out of xlog_cil_force_lsn() if we fail on xlog_write()
from a CIL push.
....
Post by Mark Tinguelyhttp://oss.sgi.com/archives/xfs/2013-12/msg00870.html
Which fell through the cracks because of objections to calling
wake_up_all(&ctx->cil->xc_commit_wait) from xlog_cil_committed().
FYI, I just independently wrote a patch to fix this, and part of the
fix is that it calls wake_up_all(&ctx->cil->xc_commit_wait) from
xlog_cil_committed(). The rest of the fix indicates that the above
patch wasn't sufficient. Patch below.
This time it isn't going to fall through the cracks because I don't
think the objections are valid...
Cheers,
Dave.
--
Dave Chinner
***@fromorbit.com
xfs: don't sleep in xlog_cil_force_lsn on shutdown
From: Dave Chinner <***@redhat.com>
Reports of a shutdown hang when fsyncing a directory have surfaced,
such as this:
[ 3663.394472] Call Trace:
[ 3663.397199] [<ffffffff815f1889>] schedule+0x29/0x70
[ 3663.402743] [<ffffffffa01feda5>] xlog_cil_force_lsn+0x185/0x1a0 [xfs]
[ 3663.416249] [<ffffffffa01fd3af>] _xfs_log_force_lsn+0x6f/0x2f0 [xfs]
[ 3663.429271] [<ffffffffa01a339d>] xfs_dir_fsync+0x7d/0xe0 [xfs]
[ 3663.435873] [<ffffffff811df8c5>] do_fsync+0x65/0xa0
[ 3663.441408] [<ffffffff811dfbc0>] SyS_fsync+0x10/0x20
[ 3663.447043] [<ffffffff815fc7d9>] system_call_fastpath+0x16/0x1b
If we trigger a shutdown in xlog_cil_push() from xlog_write(), we
will never wake waiters on the current push sequence number, so
anything waiting in xlog_cil_force_lsn() for that push sequence
number to come up will not get woken and hence stall the shutdown.
Fix this by ensuring we call wake_up_all(&cil->xc_commit_wait) in
the push abort handling, in the log shutdown code when waking all
waiters, and adding a shutdown check in the sequence completion wait
loops to ensure they abort when a wakeup due to a shutdown occurs.
Signed-off-by: Dave Chinner <***@redhat.com>
---
fs/xfs/xfs_log.c | 7 +++++--
fs/xfs/xfs_log_cil.c | 50 ++++++++++++++++++++++++++++++++++++++++++--------
2 files changed, 47 insertions(+), 10 deletions(-)
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index a5f8bd9..dbba2d7 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3952,11 +3952,14 @@ xfs_log_force_umount(
retval = xlog_state_ioerror(log);
spin_unlock(&log->l_icloglock);
}
+
/*
- * Wake up everybody waiting on xfs_log_force.
- * Callback all log item committed functions as if the
+ * Wake up everybody waiting on xfs_log_force. This needs to wake anyone
+ * waiting on a CIL push that is issued as part of a log force first
+ * before running the log item committed callback functions as if the
* log writes were completed.
*/
+ wake_up_all(&log->l_cilp->xc_commit_wait);
xlog_state_do_callback(log, XFS_LI_ABORTED, NULL);
#ifdef XFSERRORDEBUG
diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 7e54553..3a68ddf 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -385,7 +385,15 @@ xlog_cil_committed(
xfs_extent_busy_clear(mp, &ctx->busy_extents,
(mp->m_flags & XFS_MOUNT_DISCARD) && !abort);
+ /*
+ * If we are aborting the commit, wake up anyone waiting on the
+ * committing list. If we don't, then a shutdown we can leave processes
+ * waiting in xlog_cil_force_lsn() waiting on a sequence commit that
+ * will never happen because we aborted it.
+ */
spin_lock(&ctx->cil->xc_push_lock);
+ if (abort)
+ wake_up_all(&cil->xc_commit_wait);
list_del(&ctx->committing);
spin_unlock(&ctx->cil->xc_push_lock);
@@ -564,8 +572,18 @@ restart:
spin_lock(&cil->xc_push_lock);
list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
/*
+ * Avoid getting stuck in this loop because we were woken by the
+ * shutdown, but then went back to sleep once already in the
+ * shutdown state.
+ */
+ if (XLOG_FORCED_SHUTDOWN(log)) {
+ spin_unlock(&cil->xc_push_lock);
+ goto out_abort_free_ticket;
+ }
+
+ /*
* Higher sequences will wait for this one so skip them.
- * Don't wait for own own sequence, either.
+ * Don't wait for our own sequence, either.
*/
if (new_ctx->sequence >= ctx->sequence)
continue;
@@ -810,6 +828,13 @@ restart:
*/
spin_lock(&cil->xc_push_lock);
list_for_each_entry(ctx, &cil->xc_committing, committing) {
+ /*
+ * Avoid getting stuck in this loop because we were woken by the
+ * shutdown, but then went back to sleep once already in the
+ * shutdown state.
+ */
+ if (XLOG_FORCED_SHUTDOWN(log))
+ goto out_shutdown;
if (ctx->sequence > sequence)
continue;
if (!ctx->commit_lsn) {
@@ -833,14 +858,12 @@ restart:
* push sequence after the above wait loop and the CIL still contains
* dirty objects.
*
- * When the push occurs, it will empty the CIL and
- * atomically increment the currect sequence past the push sequence and
- * move it into the committing list. Of course, if the CIL is clean at
- * the time of the push, it won't have pushed the CIL at all, so in that
- * case we should try the push for this sequence again from the start
- * just in case.
+ * When the push occurs, it will empty the CIL and atomically increment
+ * the currect sequence past the push sequence and move it into the
+ * committing list. Of course, if the CIL is clean at the time of the
+ * push, it won't have pushed the CIL at all, so in that case we should
+ * try the push for this sequence again from the start just in case.
*/
-
if (sequence == cil->xc_current_sequence &&
!list_empty(&cil->xc_cil)) {
spin_unlock(&cil->xc_push_lock);
@@ -849,6 +872,17 @@ restart:
spin_unlock(&cil->xc_push_lock);
return commit_lsn;
+
+ /*
+ * We detected a shutdown in progress. We need to trigger the log force
+ * to pass through it's iclog state machine error handling, even though
+ * we are already in a shutdown state. Hence we can't return
+ * NULLCOMMITLSN here as that has special meaning to log forces (i.e.
+ * LSN is already stable), so we return a zero LSN instead.
+ */
+out_shutdown:
+ spin_unlock(&cil->xc_push_lock);
+ return 0;
}
/*