| From abab13b5c4fd1fec4f9a61622548012d93dc2831 Mon Sep 17 00:00:00 2001 |
| From: Jens Axboe <axboe@fb.com> |
| Date: Tue, 7 Oct 2014 08:39:20 -0600 |
| Subject: blk-mq: fix potential hang if rolling wakeup depth is too high |
| |
| From: Jens Axboe <axboe@fb.com> |
| |
| commit abab13b5c4fd1fec4f9a61622548012d93dc2831 upstream. |
| |
| 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 <bvanassche@acm.org> |
| Fixes: 4bb659b156996 |
| Signed-off-by: Jens Axboe <axboe@fb.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| block/blk-mq-tag.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/block/blk-mq-tag.c |
| +++ b/block/blk-mq-tag.c |
| @@ -463,8 +463,8 @@ static void bt_update_count(struct blk_m |
| } |
| |
| 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; |
| } |
