On 4/8/19 10:07 AM, jianchao.wang wrote:
> Hi Bart
>
> On 4/4/19 4:11 AM, Bart Van Assche wrote:
>> If blk_mq_try_issue_directly() returns BLK_STS*_RESOURCE that means that
>> the request has not been queued and that the caller should retry to submit
>> the request. Both blk_mq_request_bypass_insert() and
>> blk_mq_sched_insert_request() guarantee that a request will be processed.
>> Hence return BLK_STS_OK if one of these functions is called. This patch
>> avoids that blk_mq_dispatch_rq_list() crashes when using dm-mpath.
>
> Sorry, I seem to miss the original mail list that reported this issue.
> As your comment, it looks like that the request is handled again when
> the blk_mq_try_issue_directly return BLK_STS*_RESOURCE, right ?
>
> The usage of this helper interface is,
> if care about the return value and want to handle the request yourself when
> return BLK_STS*_RESOURCE, pass 'byass' as true.
> otherwise, just pass 'bypass' as false, then blk_mq_try_issue_directly would
> take over all of the work including requeue or complete the request.
>
> if dm-mpath case, the driver should only invoke dm_dispatch_clone_request,
> the 'bypass' parameter should only be true.
> as the blk_mq_try_issue_directly,
> it would return BLK_STS_OK when have to insert the request, otherwise,
> it would do nothing but return BLK_STS*_RESOURCE.
>
> Would you please show the cause that the dm-mpath driver invoke blk_mq_try_issue_direclty
> with 'bypass == false' ?
>
The issue seems to be here,
blk_mq_try_issue_directly
if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) {
run_queue = false;
bypass = false; //------> HERE !!!
goto out_unlock;
}
case BLK_STS_RESOURCE:
if (force) {
blk_mq_request_bypass_insert(rq, run_queue);
ret = bypass ? BLK_STS_OK : ret;
} else if (!bypass) {
blk_mq_sched_insert_request(rq, false,
run_queue, false);
}
break;
Then the request will be inserted and blk_mq_try_issue_dreictly returns BLK_STS_RESOURCE.
Could following patch fix the issue ?
diff --git a/block/blk-mq.c b/block/blk-mq.c
index a9c1816..a3394f2 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1813,7 +1813,7 @@ blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
*/
if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) {
run_queue = false;
- bypass = false;
+ force = true;
goto out_unlock;
}
Thanks
Jianchao
>
>>
>> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
>> Cc: Hannes Reinecke <hare@xxxxxxxx>
>> Cc: James Smart <james.smart@xxxxxxxxxxxx>
>> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
>> Cc: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
>> Cc: Keith Busch <keith.busch@xxxxxxxxx>
>> Cc: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
>> Cc: Laurence Oberman <loberman@xxxxxxxxxx>
>> Tested-by: Laurence Oberman <loberman@xxxxxxxxxx>
>> Reviewed-by: Laurence Oberman <loberman@xxxxxxxxxx>
>> Reported-by: Laurence Oberman <loberman@xxxxxxxxxx>
>> Fixes: 7f556a44e61d ("blk-mq: refactor the code of issue request directly") # v5.0.
>> Cc: <stable@xxxxxxxxxxxxxxx>
>> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
>> ---
>> block/blk-mq.c | 9 ++-------
>> 1 file changed, 2 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 652d0c6d5945..b2c20dce8a30 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -1859,16 +1859,11 @@ blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>> case BLK_STS_RESOURCE:
>> if (force) {
>> blk_mq_request_bypass_insert(rq, run_queue);
>> - /*
>> - * We have to return BLK_STS_OK for the DM
>> - * to avoid livelock. Otherwise, we return
>> - * the real result to indicate whether the
>> - * request is direct-issued successfully.
>> - */
>> - ret = bypass ? BLK_STS_OK : ret;
>> + ret = BLK_STS_OK;
>> } else if (!bypass) {
>> blk_mq_sched_insert_request(rq, false,
>> run_queue, false);
>> + ret = BLK_STS_OK;
>> }
>> break;
>> default:
>>
>
