fs-writeback: check sync bit earlier in inode_wait_for_writeback

When wb_writeback() hasn't written anything it will re-acquire the inode
lock before calling inode_wait_for_writeback.

This change tests the sync bit first so that is doesn't need to drop &
re-acquire the lock if the inode became available while wb_writeback() was
waiting to get the lock.

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5c4161f1fd9a..ea8592b90696 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -409,11 +409,11 @@ static void inode_wait_for_writeback(struct inode *inode)
         wait_queue_head_t *wqh;
 
         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
-        do {
+         while (inode->i_state & I_SYNC) {
                 spin_unlock(&inode_lock);
                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
                 spin_lock(&inode_lock);
-        } while (inode->i_state & I_SYNC);
+        }
 }
 
 /*