md/r5cache: call mddev_lock/unlock() in r5c_journal_mode_set

In r5c_journal_mode_set(), it is necessary to call mddev_lock()
before accessing conf and conf->log. Otherwise, the conf->log
may change (and become NULL).

Shaohua: fix unlock in failure cases

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 15 insertions, 6 deletions

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index bfa1e907c472..ce98414a6e34 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -2540,23 +2540,32 @@ static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
  */
 int r5c_journal_mode_set(struct mddev *mddev, int mode)
 {
-        struct r5conf *conf = mddev->private;
-        struct r5l_log *log = conf->log;
-
-        if (!log)
-                return -ENODEV;
+        struct r5conf *conf;
+        int err;
 
         if (mode < R5C_JOURNAL_MODE_WRITE_THROUGH ||
             mode > R5C_JOURNAL_MODE_WRITE_BACK)
                 return -EINVAL;
 
+        err = mddev_lock(mddev);
+        if (err)
+                return err;
+        conf = mddev->private;
+        if (!conf || !conf->log) {
+                mddev_unlock(mddev);
+                return -ENODEV;
+        }
+
         if (raid5_calc_degraded(conf) > 0 &&
-            mode == R5C_JOURNAL_MODE_WRITE_BACK)
+            mode == R5C_JOURNAL_MODE_WRITE_BACK) {
+                mddev_unlock(mddev);
                 return -EINVAL;
+        }
 
         mddev_suspend(mddev);
         conf->log->r5c_journal_mode = mode;
         mddev_resume(mddev);
+        mddev_unlock(mddev);
 
         pr_debug("md/raid:%s: setting r5c cache mode to %d: %s\n",
                  mdname(mddev), mode, r5c_journal_mode_str[mode]);