ocfs2: _really_ sync the right range

"ocfs2 syncs the wrong range" had been broken; prior to it the
code was doing the wrong thing in case of O_APPEND, all right,
but _after_ it we were syncing the wrong range in 100% cases.
*ppos, aka iocb->ki_pos is incremented prior to that point,
so we are always doing sync on the area _after_ the one we'd
written to.

Spotted by Joseph Qi <joseph.qi@huawei.com> back in January;
unfortunately, I'd missed his mail back then ;-/

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 4 deletions

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index a39067f4dd55..ba1790e52ff2 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2439,10 +2439,14 @@ out_dio:
         /* buffered aio wouldn't have proper lock coverage today */
         BUG_ON(ret == -EIOCBQUEUED && !(file->f_flags & O_DIRECT));
 
+        if (unlikely(written <= 0))
+                goto no_sync;
+
         if (((file->f_flags & O_DSYNC) && !direct_io) || IS_SYNC(inode) ||
             ((file->f_flags & O_DIRECT) && !direct_io)) {
-                ret = filemap_fdatawrite_range(file->f_mapping, *ppos,
-                                               *ppos + count - 1);
+                ret = filemap_fdatawrite_range(file->f_mapping,
+                                               iocb->ki_pos - written,
+                                               iocb->ki_pos - 1);
                 if (ret < 0)
                         written = ret;
 
@@ -2453,10 +2457,12 @@ out_dio:
                 }
 
                 if (!ret)
-                        ret = filemap_fdatawait_range(file->f_mapping, *ppos,
-                                                      *ppos + count - 1);
+                        ret = filemap_fdatawait_range(file->f_mapping,
+                                                      iocb->ki_pos - written,
+                                                      iocb->ki_pos - 1);
         }
 
+no_sync:
         /*
          * deep in g_f_a_w_n()->ocfs2_direct_IO we pass in a ocfs2_dio_end_io
          * function pointer which is called when o_direct io completes so that