elevator: acquire q->sysfs_lock in elevator_change()

Add locking of q->sysfs_lock into elevator_change() (an exported function)
to ensure it is held to protect q->elevator from elevator_init(), even if
elevator_change() is called from non-sysfs paths.
sysfs path (elv_iosched_store) uses __elevator_change(), non-locking
version, as the lock is already taken by elv_iosched_store().

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 14 insertions, 2 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 249cc5e10906..b7ff2861b6bd 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -965,7 +965,7 @@ fail_init:
 /*
  * Switch this queue to the given IO scheduler.
  */
-int elevator_change(struct request_queue *q, const char *name)
+static int __elevator_change(struct request_queue *q, const char *name)
 {
         char elevator_name[ELV_NAME_MAX];
         struct elevator_type *e;
@@ -987,6 +987,18 @@ int elevator_change(struct request_queue *q, const char *name)
 
         return elevator_switch(q, e);
 }
+
+int elevator_change(struct request_queue *q, const char *name)
+{
+        int ret;
+
+        /* Protect q->elevator from elevator_init() */
+        mutex_lock(&q->sysfs_lock);
+        ret = __elevator_change(q, name);
+        mutex_unlock(&q->sysfs_lock);
+
+        return ret;
+}
 EXPORT_SYMBOL(elevator_change);
 
 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
@@ -997,7 +1009,7 @@ ssize_t elv_iosched_store(struct request_queue *q, const char *name,
         if (!q->elevator)
                 return count;
 
-        ret = elevator_change(q, name);
+        ret = __elevator_change(q, name);
         if (!ret)
                 return count;