md/r5cache: call mddev_lock/unlock() in r5c_journal_mode_show

In r5c_journal_mode_show(), it is necessary to call mddev_lock()
before accessing conf and conf->log. Otherwise, the conf->log
may change (and become NULL).

Signed-off-by: Song Liu <songliubraving@fb.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 2dcbafa8e66c..e357ed367140 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -2529,11 +2529,18 @@ static void r5l_write_super(struct r5l_log *log, sector_t cp)
 
 static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
         int ret;
 
-        if (!conf->log)
+        ret = mddev_lock(mddev);
+        if (ret)
+                return ret;
+
+        conf = mddev->private;
+        if (!conf || !conf->log) {
+                mddev_unlock(mddev);
                 return 0;
+        }
 
         switch (conf->log->r5c_journal_mode) {
         case R5C_JOURNAL_MODE_WRITE_THROUGH:
@@ -2551,6 +2558,7 @@ static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
         default:
                 ret = 0;
         }
+        mddev_unlock(mddev);
         return ret;
 }