writeback: Fix data corruption on NFS

Commit 4f8ad655dbc8 "writeback: Refactor writeback_single_inode()" added
a condition to skip clean inode. However this is wrong in WB_SYNC_ALL
mode because there we also want to wait for outstanding writeback on
possibly clean inode. This was causing occasional data corruption issues
on NFS because it uses sync_inode() to make sure all outstanding writes
are flushed to the server before truncating the inode and with
sync_inode() returning prematurely file was sometimes extended back
by an outstanding write after it was truncated.

So modify the test to also check for pages under writeback in
WB_SYNC_ALL mode.

CC: stable@vger.kernel.org # >= 3.5
Fixes: 4f8ad655dbc82cf05d2edc11e66b78a42d38bf93
Reported-and-tested-by: Dan Duval <dan.duval@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 9 insertions, 6 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1f4a10ece2f1..e0259a163f98 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -516,13 +516,16 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
         }
         WARN_ON(inode->i_state & I_SYNC);
         /*
-         * Skip inode if it is clean. We don't want to mess with writeback
-         * lists in this function since flusher thread may be doing for example
-         * sync in parallel and if we move the inode, it could get skipped. So
-         * here we make sure inode is on some writeback list and leave it there
-         * unless we have completely cleaned the inode.
+         * Skip inode if it is clean and we have no outstanding writeback in
+         * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
+         * function since flusher thread may be doing for example sync in
+         * parallel and if we move the inode, it could get skipped. So here we
+         * make sure inode is on some writeback list and leave it there unless
+         * we have completely cleaned the inode.
          */
-        if (!(inode->i_state & I_DIRTY))
+        if (!(inode->i_state & I_DIRTY) &&
+            (wbc->sync_mode != WB_SYNC_ALL ||
+             !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
                 goto out;
         inode->i_state |= I_SYNC;
         spin_unlock(&inode->i_lock);