Re: Panic when rebooting target server testing srp on 5.0.0-rc2

[Bart Van Assche <bvanassche@acm.org>]

On Wed, 2019-03-27 at 18:00 -0400, Laurence Oberman wrote:
> Hello Jens, Jianchao
> Finally made it to this one.
> I will see if I can revert and test
> 
> 7f556a44e61d0b62d78db9a2662a5f0daef010f2 is the first bad commit
> commit 7f556a44e61d0b62d78db9a2662a5f0daef010f2
> Author: Jianchao Wang <jianchao.w.wang@oracle.com>
> Date:   Fri Dec 14 09:28:18 2018 +0800
> 
>     blk-mq: refactor the code of issue request directly
>     
>     Merge blk_mq_try_issue_directly and __blk_mq_try_issue_directly
>     into one interface to unify the interfaces to issue requests
>     directly. The merged interface takes over the requests totally,
>     it could insert, end or do nothing based on the return value of
>     .queue_rq and 'bypass' parameter. Then caller needn't any other
>     handling any more and then code could be cleaned up.
>     
>     And also the commit c616cbee ( blk-mq: punt failed direct issue
>     to dispatch list ) always inserts requests to hctx dispatch list
>     whenever get a BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE, this is
>     overkill and will harm the merging. We just need to do that for
>     the requests that has been through .queue_rq. This patch also
>     could fix this.
>     
>     Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
>     Signed-off-by: Jens Axboe <axboe@kernel.dk>

Hi Laurence,

I have not been able to reproduce this issue. But you may want to try
the following patch (applies on top of v5.1-rc3):


Subject: [PATCH] block: Fix blk_mq_try_issue_directly()

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.

Reported-by: Laurence Oberman <loberman@redhat.com>
Fixes: 7f556a44e61d ("blk-mq: refactor the code of issue request directly") # v5.0.
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:


Thanks,

Bart.