[XFS] Sleeping with the ilock waiting for I/O completion is Bad.

Recent fixes to the filesystem freezing code introduced a vn_iowait call
in the middle of the sync code. Unfortunately, at the point where this
call was added we are holding the ilock. The ilock is needed by I/O
completion for unwritten extent conversion and now updating the file size.
Hence I/o cannot complete if we hold the ilock while waiting for I/O
completion.

Fix up the bug and clean the code up around it.

SGI-PV: 963674
SGI-Modid: xfs-linux-melb:xfs-kern:28566a
Signed-off-by: NDavid Chinner <dgc@sgi.com>
Signed-off-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NTim Shimmin <tes@sgi.com>

fs/xfs/xfs_vfsops.c

@@ -1128,58 +1128,41 @@ xfs_sync_inodes(
 		 * in the inode list.
 		 */
 
-		if ((flags & SYNC_CLOSE)  && (vp != NULL)) {
-			/*
-			 * This is the shutdown case.  We just need to
-			 * flush and invalidate all the pages associated
-			 * with the inode.  Drop the inode lock since
-			 * we can't hold it across calls to the buffer
-			 * cache.
-			 *
-			 * We don't set the VREMAPPING bit in the vnode
-			 * here, because we don't hold the vnode lock
-			 * exclusively.  It doesn't really matter, though,
-			 * because we only come here when we're shutting
-			 * down anyway.
-			 */
-			xfs_iunlock(ip, XFS_ILOCK_SHARED);
-
-			if (XFS_FORCED_SHUTDOWN(mp)) {
-				bhv_vop_toss_pages(vp, 0, -1, FI_REMAPF);
-			} else {
-				error = bhv_vop_flushinval_pages(vp, 0, -1, FI_REMAPF);
+		/*
+		 * If we have to flush data or wait for I/O completion
+		 * we need to drop the ilock that we currently hold.
+		 * If we need to drop the lock, insert a marker if we
+		 * have not already done so.
+		 */
+		if ((flags & (SYNC_CLOSE|SYNC_IOWAIT)) ||
+		    ((flags & SYNC_DELWRI) && VN_DIRTY(vp))) {
+			if (mount_locked) {
+				IPOINTER_INSERT(ip, mp);
 			}
+			xfs_iunlock(ip, XFS_ILOCK_SHARED);
 
-			xfs_ilock(ip, XFS_ILOCK_SHARED);
-
-		} else if ((flags & SYNC_DELWRI) && (vp != NULL)) {
-			if (VN_DIRTY(vp)) {
-				/* We need to have dropped the lock here,
-				 * so insert a marker if we have not already
-				 * done so.
-				 */
-				if (mount_locked) {
-					IPOINTER_INSERT(ip, mp);
-				}
-
-				/*
-				 * Drop the inode lock since we can't hold it
-				 * across calls to the buffer cache.
-				 */
-				xfs_iunlock(ip, XFS_ILOCK_SHARED);
+			if (flags & SYNC_CLOSE) {
+				/* Shutdown case. Flush and invalidate. */
+				if (XFS_FORCED_SHUTDOWN(mp))
+					bhv_vop_toss_pages(vp, 0, -1, FI_REMAPF);
+				else
+					error = bhv_vop_flushinval_pages(vp, 0,
+								-1, FI_REMAPF);
+			} else if ((flags & SYNC_DELWRI) && VN_DIRTY(vp)) {
 				error = bhv_vop_flush_pages(vp, (xfs_off_t)0,
 							-1, fflag, FI_NONE);
-				xfs_ilock(ip, XFS_ILOCK_SHARED);
 			}
 
+			/*
+			 * When freezing, we need to wait ensure all I/O (including direct
+			 * I/O) is complete to ensure no further data modification can take
+			 * place after this point
+			 */
+			if (flags & SYNC_IOWAIT)
+				vn_iowait(vp);
+
+			xfs_ilock(ip, XFS_ILOCK_SHARED);
 		}
-		/*
-		 * When freezing, we need to wait ensure all I/O (including direct
-		 * I/O) is complete to ensure no further data modification can take
-		 * place after this point
-		 */
-		if (flags & SYNC_IOWAIT)
-			vn_iowait(vp);
 
 		if (flags & SYNC_BDFLUSH) {
 			if ((flags & SYNC_ATTR) &&