From: Jan Kara <jack@suse.cz>
Date: Tue, 11 Apr 2017 09:29:01 +0000 (+0200)
Subject: block: Fix list corruption of blk stats callback list
X-Git-Tag: v4.12-rc1~119^2~167
X-Git-Url: http://git.samba.org/samba.git/?p=sfrench%2Fcifs-2.6.git;a=commitdiff_plain;h=3f19cd23f3a9420fe7bd98ad41d05e45fa6d4d47

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 ffa80e11cf14..b3b79149d3a0 100644
--- 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);