From abab13b5c4fd1fec4f9a61622548012d93dc2831 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 7 Oct 2014 08:39:20 -0600 Subject: blk-mq: fix potential hang if rolling wakeup depth is too high We currently divide the queue depth by 4 as our batch wakeup count, but we split the wakeups over BT_WAIT_QUEUES number of wait queues. This defaults to 8. If the product of the resulting batch wake count and BT_WAIT_QUEUES is higher than the device queue depth, we can get into a situation where a task goes to sleep waiting for a request, but never gets woken up. Reported-by: Bart Van Assche Fixes: 4bb659b156996 Cc: stable@kernel.org Signed-off-by: Jens Axboe --- block/blk-mq-tag.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'block') diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index b08788086414..146fd02659ec 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -455,8 +455,8 @@ static void bt_update_count(struct blk_mq_bitmap_tags *bt, } bt->wake_cnt = BT_WAIT_BATCH; - if (bt->wake_cnt > depth / 4) - bt->wake_cnt = max(1U, depth / 4); + if (bt->wake_cnt > depth / BT_WAIT_QUEUES) + bt->wake_cnt = max(1U, depth / BT_WAIT_QUEUES); bt->depth = depth; } -- cgit v1.2.3