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blk-mq: fix potential hang if rolling wakeup depth is too high

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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: 4bb659b156
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Jens Axboe 2014-10-07 08:39:20 -06:00
parent d8f429e166
commit abab13b5c4
1 changed files with 2 additions and 2 deletions
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4
block/blk-mq-tag.c
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@ -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;
}