Re: [PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[Daniel Wagner <dwagner@suse.de>]

Hi,

On Mon, Jul 26, 2021 at 02:14:30PM +0000, Wen Xiong wrote:
> >>V6 is basically same with V4, can you figure out where the failure
> >>comes?(v5.14-rc2, V6 or Daniel's V3)
>  
> Looks 3/3 was not patched cleanly in v5.14-rc2 last week.  I made the changes
> in block/blk-mq.c.rej manually but still missed the last part of 3/3 patch.

Sorry for the long delay on my side. It took a while to get my test
setup running again. The qla2xxx driver really doesn't like 'fast'
remote port toggling. But that's a different story.

Anyway, it turns out that my patch series is still not working
correctly. When I tested the series I deliberate forced to execute
the 'revising io queue count' path in nvme_fc_recreate_io_queues by
doing:

--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -2954,7 +2954,7 @@ nvme_fc_recreate_io_queues(struct nvme_fc_ctrl *ctrl)
        if (ctrl->ctrl.queue_count == 1)
                return 0;
 
-       if (prior_ioq_cnt != nr_io_queues) {
+       if (prior_ioq_cnt != nr_io_queues - 1) {
                dev_info(ctrl->ctrl.device,
                        "reconnect: revising io queue count from %d to %d\n",
                        prior_ioq_cnt, nr_io_queues);


With this change I can't observe any I/O hanging. Without the change it
hangs in the first iteration.

In Wen's setup we observed in earlier debugging sessions that the
nr_io_queues does change. So this explains why Wen doesn't see any
hanging I/Os.

@James, I think we need to look at bit more at the freeze code. BTW,
my initial patch which just added a nvme_start_freeze() in
nvme_fc_delete_association() doesn't work either for the 'prior_ioq_cnt
== nr_io_queues' case.

So I think Ming series can be merged as the hanging I/Os are clearly not
caused by the series.

Feel free to add

Tested-by: Daniel Wagner <dwagner@suse.de>

Thanks,
Daniel