[PATCH 3.16 013/410] f2fs: fix a panic caused by NULL flush_cmd_control

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Yunlei He <heyunlei@xxxxxxxxxx>

commit d4fdf8ba0e5808ba9ad6b44337783bd9935e0982 upstream.

Mount fs with option noflush_merge, boot failed for illegal address
fcc in function f2fs_issue_flush:

        if (!test_opt(sbi, FLUSH_MERGE)) {
                ret = submit_flush_wait(sbi);
                atomic_inc(&fcc->issued_flush);   ->  Here, fcc illegal
                return ret;
        }

Signed-off-by: Yunlei He <heyunlei@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/f2fs/segment.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -273,6 +273,9 @@ int create_flush_cmd_control(struct f2fs
 	spin_lock_init(&fcc->issue_lock);
 	init_waitqueue_head(&fcc->flush_wait_queue);
 	sbi->sm_info->cmd_control_info = fcc;
+	if (!test_opt(sbi, FLUSH_MERGE))
+		return err;
+
 	fcc->f2fs_issue_flush = kthread_run(issue_flush_thread, sbi,
 				"f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
 	if (IS_ERR(fcc->f2fs_issue_flush)) {
@@ -1905,7 +1908,7 @@ int build_segment_manager(struct f2fs_sb
 	sm_info->nr_discards = 0;
 	sm_info->max_discards = 0;
 
-	if (test_opt(sbi, FLUSH_MERGE) && !f2fs_readonly(sbi->sb)) {
+	if (!f2fs_readonly(sbi->sb)) {
 		err = create_flush_cmd_control(sbi);
 		if (err)
 			return err;