[Devel] [PATCH RH7] block: Fix list corruption of blk stats callback list

[Pavel Tikhomirov]

From: Jan Kara <jack at suse.cz>

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 at suse.cz>
Signed-off-by: Jens Axboe <axboe at fb.com>

https://jira.sw.ru/browse/PSBM-99021

(cherry picked from commit 3f19cd23f3a9420fe7bd98ad41d05e45fa6d4d47)
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

---
 block/blk-wbt.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 554f4ee970c7..67f0c9e6451f 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -648,19 +648,15 @@ 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) {
-		blk_stat_remove_callback(q, rwb->cb);
-		rwb->win_nsec = rwb->min_lat_nsec = 0;
-		wbt_update_limits(rwb);
-	}
+	if (rwb)
+		wbt_exit(q);
 }
 EXPORT_SYMBOL_GPL(wbt_disable_default);
 
-- 
2.21.0