[XFS] Block on unwritten extent conversion during synchronous direct I/O.

Currently we do not wait on extent conversion to occur, and hence we can
return to userspace from a synchronous direct I/O write without having
completed all the actions in the write. Hence a read after the write may
see zeroes (unwritten extent) rather than the data that was written.

Block the I/O completion by triggering a synchronous workqueue flush to
ensure that the conversion has occurred before we return to userspace.

SGI-PV: 964092
SGI-Modid: xfs-linux-melb:xfs-kern:28775a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

1 files changed, 20 insertions, 8 deletions

diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 7361861e3aac..80a321462315 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -108,14 +108,19 @@ xfs_page_trace(
 
 /*
  * Schedule IO completion handling on a xfsdatad if this was
- * the final hold on this ioend.
+ * the final hold on this ioend. If we are asked to wait,
+ * flush the workqueue.
  */
 STATIC void
 xfs_finish_ioend(
-        xfs_ioend_t             *ioend)
+        xfs_ioend_t     *ioend,
+        int             wait)
 {
-        if (atomic_dec_and_test(&ioend->io_remaining))
+        if (atomic_dec_and_test(&ioend->io_remaining)) {
                 queue_work(xfsdatad_workqueue, &ioend->io_work);
+                if (wait)
+                        flush_workqueue(xfsdatad_workqueue);
+        }
 }
 
 /*
@@ -334,7 +339,7 @@ xfs_end_bio(
         bio->bi_end_io = NULL;
         bio_put(bio);
 
-        xfs_finish_ioend(ioend);
+        xfs_finish_ioend(ioend, 0);
         return 0;
 }
 
@@ -470,7 +475,7 @@ xfs_submit_ioend(
                 }
                 if (bio)
                         xfs_submit_ioend_bio(ioend, bio);
-                xfs_finish_ioend(ioend);
+                xfs_finish_ioend(ioend, 0);
         } while ((ioend = next) != NULL);
 }
 
@@ -1416,6 +1421,13 @@ xfs_end_io_direct(
          * This is not necessary for synchronous direct I/O, but we do
          * it anyway to keep the code uniform and simpler.
          *
+         * Well, if only it were that simple. Because synchronous direct I/O
+         * requires extent conversion to occur *before* we return to userspace,
+         * we have to wait for extent conversion to complete. Look at the
+         * iocb that has been passed to us to determine if this is AIO or
+         * not. If it is synchronous, tell xfs_finish_ioend() to kick the
+         * workqueue and wait for it to complete.
+         *
          * The core direct I/O code might be changed to always call the
          * completion handler in the future, in which case all this can
          * go away.
@@ -1423,9 +1435,9 @@ xfs_end_io_direct(
         ioend->io_offset = offset;
         ioend->io_size = size;
         if (ioend->io_type == IOMAP_READ) {
-                xfs_finish_ioend(ioend);
+                xfs_finish_ioend(ioend, 0);
         } else if (private && size > 0) {
-                xfs_finish_ioend(ioend);
+                xfs_finish_ioend(ioend, is_sync_kiocb(iocb));
         } else {
                 /*
                  * A direct I/O write ioend starts it's life in unwritten
@@ -1434,7 +1446,7 @@ xfs_end_io_direct(
                  * handler.
                  */
                 INIT_WORK(&ioend->io_work, xfs_end_bio_written);
-                xfs_finish_ioend(ioend);
+                xfs_finish_ioend(ioend, 0);
         }
 
         /*