xfs: initialize log buf I/O completion wq on log alloc

Log buffer I/O completion passes through the high priority
m_log_workqueue rather than the default metadata buffer workqueue. The
log buffer wq is initialized at I/O submission time. The log buffers are
reused once initialized, however, so this is not necessary.

Initialize the log buffer I/O completion workqueue pointers once when
the log is allocated and log buffers initialized rather than on every
log buffer I/O submission.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_log.c

@@ -1395,6 +1395,8 @@ xlog_alloc_log(
 	ASSERT(xfs_buf_islocked(bp));
 	xfs_buf_unlock(bp);
 
+	/* use high priority wq for log I/O completion */
+	bp->b_ioend_wq = mp->m_log_workqueue;
 	bp->b_iodone = xlog_iodone;
 	log->l_xbuf = bp;
 
@@ -1427,6 +1429,8 @@ xlog_alloc_log(
 		ASSERT(xfs_buf_islocked(bp));
 		xfs_buf_unlock(bp);
 
+		/* use high priority wq for log I/O completion */
+		bp->b_ioend_wq = mp->m_log_workqueue;
 		bp->b_iodone = xlog_iodone;
 		iclog->ic_bp = bp;
 		iclog->ic_data = bp->b_addr;
@@ -1806,8 +1810,6 @@ xlog_sync(
 	XFS_BUF_ZEROFLAGS(bp);
 	XFS_BUF_ASYNC(bp);
 	bp->b_flags |= XBF_SYNCIO;
-	/* use high priority completion wq */
-	bp->b_ioend_wq = log->l_mp->m_log_workqueue;
 
 	if (log->l_mp->m_flags & XFS_MOUNT_BARRIER) {
 		bp->b_flags |= XBF_FUA;
@@ -1856,8 +1858,6 @@ xlog_sync(
 		bp->b_flags |= XBF_SYNCIO;
 		if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)
 			bp->b_flags |= XBF_FUA;
-		/* use high priority completion wq */
-		bp->b_ioend_wq = log->l_mp->m_log_workqueue;
 
 		ASSERT(XFS_BUF_ADDR(bp) <= log->l_logBBsize-1);
 		ASSERT(XFS_BUF_ADDR(bp) + BTOBB(count) <= log->l_logBBsize);