Re: [PATCH] block: quiesce queue before freeing queue

[Yufen Yu <yuyufen@huawei.com>]

On 2021/1/15 15:35, Ming Lei wrote:
> On Fri, Jan 15, 2021 at 01:43:52AM -0500, Yufen Yu wrote:
>> There is a race beteewn blk_mq_run_hw_queue() and cleanup queue,
>> which can cause use-after-free as following:

>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 7663a9b94b80..f8a038d19c89 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -392,6 +392,18 @@ void blk_cleanup_queue(struct request_queue *q)
>>   
>>   	blk_queue_flag_set(QUEUE_FLAG_DEAD, q);
>>   
>> +	/*
>> +	 * make sure all in-progress dispatch are completed because
>> +	 * blk_freeze_queue() can only complete all requests, and
>> +	 * dispatch may still be in-progress since we dispatch requests
>> +	 * from more than one contexts.
>> +	 *
>> +	 * We rely on driver to deal with the race in case that queue
>> +	 * initialization isn't done.
>> +	 */
>> +	if (queue_is_mq(q) && blk_queue_init_done(q))
>> +		blk_mq_quiesce_queue(q);
> 
> No, please don't do that. We had several slow boot reports before caused by
> by synchronize_rcu() in blk_cleanup_queue(), since blk_cleanup_queue()
> is called for in-existed queues, which number can be quite big.

Thanks to point out this. But, can't blk_queue_init_done will avoid calling
synchronize_rcu() for inexistent queues?

Thanks,
Yufen