xfs: prevent unwritten extent conversion from blocking I/O completion

Unwritten extent conversion can recurse back into the filesystem due
to memory allocation. Memory reclaim requires I/O completions to be
processed to allow the callers to make progress. If the I/O
completion workqueue thread is doing the recursion, then we have a
deadlock situation.

Move unwritten extent completion into it's own workqueue so it
doesn't block I/O completions for normal delayed allocation or
overwrite data.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index aa1016bb9134..e28800a9f2b5 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -51,6 +51,7 @@ static struct shrinker xfs_buf_shake = {
 
 static struct workqueue_struct *xfslogd_workqueue;
 struct workqueue_struct *xfsdatad_workqueue;
+struct workqueue_struct *xfsconvertd_workqueue;
 
 #ifdef XFS_BUF_TRACE
 void
@@ -1775,6 +1776,7 @@ xfs_flush_buftarg(
         xfs_buf_t       *bp, *n;
         int             pincount = 0;
 
+        xfs_buf_runall_queues(xfsconvertd_workqueue);
         xfs_buf_runall_queues(xfsdatad_workqueue);
         xfs_buf_runall_queues(xfslogd_workqueue);
 
@@ -1831,9 +1833,15 @@ xfs_buf_init(void)
         if (!xfsdatad_workqueue)
                 goto out_destroy_xfslogd_workqueue;
 
+        xfsconvertd_workqueue = create_workqueue("xfsconvertd");
+        if (!xfsconvertd_workqueue)
+                goto out_destroy_xfsdatad_workqueue;
+
         register_shrinker(&xfs_buf_shake);
         return 0;
 
+ out_destroy_xfsdatad_workqueue:
+        destroy_workqueue(xfsdatad_workqueue);
  out_destroy_xfslogd_workqueue:
         destroy_workqueue(xfslogd_workqueue);
  out_free_buf_zone:
@@ -1849,6 +1857,7 @@ void
 xfs_buf_terminate(void)
 {
         unregister_shrinker(&xfs_buf_shake);
+        destroy_workqueue(xfsconvertd_workqueue);
         destroy_workqueue(xfsdatad_workqueue);
         destroy_workqueue(xfslogd_workqueue);
         kmem_zone_destroy(xfs_buf_zone);