[PATCH 13/15] writeback: restart bdi list scan on allocation failure

[Jens Axboe <jens.axboe@oracle.com>]

It's should essentially almost never trigger, so it doesn't matter
if we just restart the scan and potentially do a bit more IO in
this case. And then we can drop bdi_lock before going into inode
sync.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 65ca410..d646e02 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -517,6 +517,7 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 	struct bdi_work *work;
 	LIST_HEAD(list);
 
+restart:
 	mutex_lock(&bdi_lock);
 
 	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
@@ -533,9 +534,13 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 		 */
 		work = bdi_alloc_work(sb, wbc->nr_to_write, wbc->sync_mode);
 		if (!work) {
+			if (!must_wait)
+				continue;
+
+			mutex_unlock(&bdi_lock);
 			wbc->bdi = bdi;
 			generic_sync_bdi_inodes(sb, wbc);
-			continue;
+			goto restart;
 		}
 		if (must_wait)
 			list_add_tail(&work->wait_list, &list);
-- 
1.6.3.rc0.1.gf800