Re: [PATCH 4/5] blk-mq-debugfs: Show busy requests

[Jens Axboe <axboe@kernel.dk>]

On 05/26/2017 03:17 PM, Bart Van Assche wrote:
> On Fri, 2017-05-26 at 07:26 -0600, Jens Axboe wrote:
>> On 05/25/2017 05:38 PM, Bart Van Assche wrote:
>>> Requests that got stuck in a block driver are neither on
>>> blk_mq_ctx.rq_list nor on any hw dispatch queue. Make these
>>> visible in debugfs through the "busy" attribute.
>>>
>>> Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
>>> Cc: Christoph Hellwig <hch@lst.de>
>>> Cc: Hannes Reinecke <hare@suse.com>
>>> Cc: Omar Sandoval <osandov@fb.com>
>>> Cc: Ming Lei <ming.lei@redhat.com>
>>> ---
>>>  block/blk-mq-debugfs.c | 25 +++++++++++++++++++++++++
>>>  1 file changed, 25 insertions(+)
>>>
>>> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
>>> index 8b06a12c1461..70a2b955afee 100644
>>> --- a/block/blk-mq-debugfs.c
>>> +++ b/block/blk-mq-debugfs.c
>>> @@ -370,6 +370,30 @@ static const struct seq_operations hctx_dispatch_seq_ops = {
>>>  	.show	= blk_mq_debugfs_rq_show,
>>>  };
>>>  
>>> +struct show_busy_ctx {
>>> +	struct seq_file		*m;
>>> +	struct blk_mq_hw_ctx	*hctx;
>>> +};
>>> +
>>> +static void hctx_show_busy(struct request *rq, void *data, bool reserved)
>>> +{
>>> +	const struct show_busy_ctx *ctx = data;
>>
>> Let's not call that variable 'ctx', in blk-mq that's pretty much
>> reserved for the sw queues.
> 
> Hello Jens,
> 
> How about renaming show_busy_ctx into show_busy_params and ctx into params?

I think that would be an improvement. Also, this:

	blk_mq_debugfs_rq_show(ctx->m, &rq->queuelist);

doesn't look safe at all, as you are passing in a node instead of a
head. I think you just want to use __blk_mq_debugfs_rq_show() here.

-- 
Jens Axboe