Re: blk-mq: make sure that correct hctx->dispatch_from is set

[Jens Axboe <axboe@kernel.dk>]

On 5/18/18 8:27 AM, Jens Axboe wrote:
> On 5/18/18 7:42 AM, 胡海 wrote:
>> Author: huhai <huhai@kylinos.cn>
>> Date:   Fri May 18 17:09:56 2018 +0800
>>
>>     blk-mq: make sure that correct hctx->dispatch_from is set
>>     
>>     When the number of hardware queues is changed, the drivers will call
>>     blk_mq_update_nr_hw_queues() to remap hardware queues, and then
>>     the ctx mapped on hctx will also change, but the current code forgets to
>>     make sure that correct hctx->dispatch_from is set, and hctx->dispatch_from
>>     may point to a ctx that does not belong to the current hctx.
> 
> Looks good, thanks. One minor note for future patches - for cases like this,
> when the patch fixes an issue with a specific commit, add a fixes line.
> For this one, it would be:
> 
> Fixes: b347689ffbca ("blk-mq-sched: improve dispatching from sw queue")

Two more notes... Your patches are still coming through as base64 encoded,
they should just be plain text.

Finally, I think the below is much clearer, since that's the loop where
we clear any existing hctx context.


diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6c6aef44badd..4cbfd784e837 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2358,6 +2358,7 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 	queue_for_each_hw_ctx(q, hctx, i) {
 		cpumask_clear(hctx->cpumask);
 		hctx->nr_ctx = 0;
+		hctx->dispatch_from = NULL;
 	}
 
 	/*

-- 
Jens Axboe