f2fs: avoid to access NULL pointer in issue_flush_thread

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=75861

Denis 2014-05-10 11:28:59 UTC reported:
"F2FS-fs (mmcblk0p28): mounting..
 Unable to handle kernel NULL pointer dereference at virtual address 00000018
 ...
 [<c0a2f678>] (_raw_spin_lock+0x3c/0x70) from [<c03a0330>] (issue_flush_thread+0x50/0x17c)
 [<c03a0330>] (issue_flush_thread+0x50/0x17c) from [<c01b4064>] (kthread+0x98/0xa4)
 [<c01b4064>] (kthread+0x98/0xa4) from [<c0108060>] (kernel_thread_exit+0x0/0x8)"

This patch assign cmd_control_info in sm_info before issue_flush_thread is being
created, so this make sure that issue flush thread will have no chance to access
invalid info in fcc.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Reviewed-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index b22d5a0652bb..d04613df710a 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -272,14 +272,15 @@ int create_flush_cmd_control(struct f2fs_sb_info *sbi)
                 return -ENOMEM;
         spin_lock_init(&fcc->issue_lock);
         init_waitqueue_head(&fcc->flush_wait_queue);
+        sbi->sm_info->cmd_control_info = fcc;
         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)) {
                 err = PTR_ERR(fcc->f2fs_issue_flush);
                 kfree(fcc);
+                sbi->sm_info->cmd_control_info = NULL;
                 return err;
         }
-        sbi->sm_info->cmd_control_info = fcc;
 
         return err;
 }