Re: [PATCH] block: Fix blk_mq_try_issue_directly()

[Laurence Oberman <loberman@redhat.com>]

On Tue, 2019-04-09 at 09:31 +0800, jianchao.wang wrote:
> 
> On 4/8/19 10:36 AM, jianchao.wang wrote:
> > 
> > 
> > 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 ?
> 
> Hi Laurence
> 
> Would you please test this patch to see whether the issue could be
> fixed ?
> 
> Thanks
> Jianchao
> > 
> > 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@infradead.org>
> > > > Cc: Hannes Reinecke <hare@suse.com>
> > > > Cc: James Smart <james.smart@broadcom.com>
> > > > Cc: Ming Lei <ming.lei@redhat.com>
> > > > Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
> > > > Cc: Keith Busch <keith.busch@intel.com>
> > > > Cc: Dongli Zhang <dongli.zhang@oracle.com>
> > > > Cc: Laurence Oberman <loberman@redhat.com>
> > > > Tested-by: Laurence Oberman <loberman@redhat.com>
> > > > Reviewed-by: Laurence Oberman <loberman@redhat.com>
> > > > Reported-by: Laurence Oberman <loberman@redhat.com>
> > > > Fixes: 7f556a44e61d ("blk-mq: refactor the code of issue
> > > > request directly") # v5.0.
> > > > Cc: <stable@vger.kernel.org>
> > > > Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> > > > ---
> > > >  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:
> > > > 
Hello Sir
I think Jens already took the revert patch though.
I will try this when I gat a chance.
Need to wait until I can reboot the targetserver again.
Regards
Laurence