[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>
diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 7361861..80a3214 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -108,14 +108,19 @@
/*
* 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 @@
bio->bi_end_io = NULL;
bio_put(bio);
- xfs_finish_ioend(ioend);
+ xfs_finish_ioend(ioend, 0);
return 0;
}
@@ -470,7 +475,7 @@
}
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 @@
* 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 @@
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 @@
* handler.
*/
INIT_WORK(&ioend->io_work, xfs_end_bio_written);
- xfs_finish_ioend(ioend);
+ xfs_finish_ioend(ioend, 0);
}
/*