f2fs: fix a deadlock in fsync

This patch fixes a deadlock bug that occurs quite often when there are
concurrent write and fsync on a same file.

Following is the simplified call trace when tasks get hung.

fsync thread:
- f2fs_sync_file
 ...
 - f2fs_write_data_pages
 ...
  - update_extent_cache
  ...
   - update_inode
    - wait_on_page_writeback

bdi writeback thread
- __writeback_single_inode
 - f2fs_write_data_pages
  - mutex_lock(sbi->writepages)

The deadlock happens when the fsync thread waits on a inode page that has
been added to the f2fs' cached bio sbi->bio[NODE], and unfortunately,
no one else could be able to submit the cached bio to block layer for
writeback. This is because the fsync thread already hold a sbi->fs_lock and
the sbi->writepages lock, causing the bdi thread being blocked when attempt
to write data pages for the same inode. At the same time, f2fs_gc thread
does not notice the situation and could not help. Even the sync syscall
gets blocked.

To fix it, we could submit the cached bio first before waiting on a inode page
that is being written back.

Signed-off-by: Jin Xu <jinuxstyle@gmail.com>
[Jaegeuk Kim: add more cases to use f2fs_wait_on_page_writeback]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index debf743..9ab81e7 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -151,7 +151,7 @@ void update_inode(struct inode *inode, struct page *node_page)
 	struct f2fs_node *rn;
 	struct f2fs_inode *ri;
 
-	wait_on_page_writeback(node_page);
+	f2fs_wait_on_page_writeback(node_page, NODE, false);
 
 	rn = F2FS_NODE(node_page);
 	ri = &(rn->i);