block: Fix list corruption of blk stats callback list

When CFQ calls wbt_disable_default(), it will call
blk_stat_remove_callback() to stop gathering IO statistics for the
purposes of writeback throttling. Later, when request_queue is
unregistered, wbt_exit() will call blk_stat_remove_callback() again
which will try to delete callback from the list again and possibly cause
list corruption.

Fix the problem by making wbt_disable_default() called wbt_exit() which
is properly guarded against being called multiple times.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index ffa80e11cf142fbaba109e144e115aa9255f8456..b3b79149d3a0c61529983bb5e28e62f8c25d78a9 100644 (file)
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -653,19 +653,15 @@ void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on)
                rwb->wc = write_cache_on;
 }
 
- /*
- * Disable wbt, if enabled by default. Only called from CFQ, if we have
- * cgroups enabled
+/*
+ * Disable wbt, if enabled by default. Only called from CFQ.
  */
 void wbt_disable_default(struct request_queue *q)
 {
        struct rq_wb *rwb = q->rq_wb;
 
-       if (rwb && rwb->enable_state == WBT_STATE_ON_DEFAULT) {
-               blk_stat_remove_callback(q, rwb->cb);
-               rwb->win_nsec = rwb->min_lat_nsec = 0;
-               wbt_update_limits(rwb);
-       }
+       if (rwb && rwb->enable_state == WBT_STATE_ON_DEFAULT)
+               wbt_exit(q);
 }
 EXPORT_SYMBOL_GPL(wbt_disable_default);