xfs: avoid unnecessary waits in xfs_log_force_lsn()

mainline-inclusion
from mainline-v5.14-rc1
commit 8191d822
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4KIAO
CVE: NA

Reference:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8191d8222c514c69a8e1ac46bd9812b9e0aab7d0

-------------------------------------------------
xfs: avoid unnecessary waits in xfs_log_force_lsn()

Before waiting on a iclog in xfs_log_force_lsn(), we don't check to
see if the iclog has already been completed and the contents on
stable storage. We check for completed iclogs in xfs_log_force(), so
we should do the same thing for xfs_log_force_lsn().

This fixed some random up-to-30s pauses seen in unmounting
filesystems in some tests. A log force ends up waiting on completed
iclog, and that doesn't then get flushed (and hence the log force
get completed) until the background log worker issues a log force
that flushes the iclog in question. Then the unmount unblocks and
continues.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NGuo Xuenan <guoxuenan@huawei.com>
Reviewed-by: NLihong Kou <koulihong@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/xfs/xfs_log.c

@@ -3050,6 +3050,35 @@ xlog_state_switch_iclogs(
 	log->l_iclog = iclog->ic_next;
 }
 
+/*
+ * Force the iclog to disk and check if the iclog has been completed before
+ * xlog_force_iclog() returns. This can happen on synchronous (e.g.
+ * pmem) or fast async storage because we drop the icloglock to issue the IO.
+ * If completion has already occurred, tell the caller so that it can avoid an
+ * unnecessary wait on the iclog.
+ */
+static int
+xlog_force_and_check_iclog(
+	struct xlog_in_core	*iclog,
+	bool			*completed)
+{
+	xfs_lsn_t		lsn = be64_to_cpu(iclog->ic_header.h_lsn);
+	int			error;
+
+	*completed = false;
+	error = xlog_force_iclog(iclog);
+	if (error)
+		return error;
+
+	/*
+	 * If the iclog has already been completed and reused the header LSN
+	 * will have been rewritten by completion
+	 */
+	if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
+		*completed = true;
+	return 0;
+}
+
 /*
  * Write out all data in the in-core log as of this exact moment in time.
  *
@@ -3084,7 +3113,6 @@ xfs_log_force(
 {
 	struct xlog		*log = mp->m_log;
 	struct xlog_in_core	*iclog;
-	xfs_lsn_t		lsn;
 
 	XFS_STATS_INC(mp, xs_log_force);
 	trace_xfs_log_force(mp, 0, _RET_IP_);
@@ -3111,11 +3139,12 @@ xfs_log_force(
 	} else if (iclog->ic_state == XLOG_STATE_ACTIVE) {
 		if (atomic_read(&iclog->ic_refcnt) == 0) {
 			/* We have exclusive access to this iclog. */
-			lsn = be64_to_cpu(iclog->ic_header.h_lsn);
-			if (xlog_force_iclog(iclog))
+			bool	completed;
+
+			if (xlog_force_and_check_iclog(iclog, &completed))
 				goto out_error;
 
-			if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
+			if (completed)
 				goto out_unlock;
 		} else {
 			/*
@@ -3155,6 +3184,7 @@ xlog_force_lsn(
 	bool			already_slept)
 {
 	struct xlog_in_core	*iclog;
+	bool			completed;
 
 	spin_lock(&log->l_icloglock);
 	iclog = log->l_iclog;
@@ -3191,10 +3221,12 @@ xlog_force_lsn(
 					&log->l_icloglock);
 			return -EAGAIN;
 		}
-		if (xlog_force_iclog(iclog))
+		if (xlog_force_and_check_iclog(iclog, &completed))
 			goto out_error;
 		if (log_flushed)
 			*log_flushed = 1;
+		if (completed)
+			goto out_unlock;
 		break;
 	case XLOG_STATE_WANT_SYNC:
 		/*