Re: [RFC PATCH 0/4] nvme-tcp: fix hung issues for deleting

[许春光]

Sagi Grimberg <sagi@xxxxxxxxxxx> 于2023年6月6日周二 07:09写道：
>
>
> > From: Chunguang Xu <chunguang.xu@xxxxxxxxxx>
> >
> > We found that nvme_remove_namespaces() may hang in flush_work(&ctrl->scan_work)
> > while removing ctrl. The root cause may due to the state of ctrl changed to
> > NVME_CTRL_DELETING while removing ctrl , which intterupt nvme_tcp_error_recovery_work()/
> > nvme_reset_ctrl_work()/nvme_tcp_reconnect_or_remove().  At this time, ctrl is
> > freezed and queue is quiescing . Since scan_work may continue to issue IOs to
> > load partition table, make it blocked, and lead to nvme_tcp_error_recovery_work()
> > hang in flush_work(&ctrl->scan_work).
> >
> > After analyzation, we found that there are mainly two case:
> > 1. Since ctrl is freeze, scan_work hang in __bio_queue_enter() while it issue
> >     new IO to load partition table.
> > 2. Since queus is quiescing, requeue timeouted IO may hang in hctx->dispatch
> >     queue, leading scan_work waiting for IO completion.
>
> Hey, can you please look at the discussion with Mings' proposal in
> "nvme: add nvme_delete_dead_ctrl for avoiding io deadlock" ?

Hi grimberg:

I have read Ming's patch, it seems that MIng fixed the case my patchset missed,
Ming  fixes the hang occur while reconnect fails(reach max retries), my patchset
fixes the issue that while driver processing error_recover or reconnect(have not
reach max retries), user actively remove ctrl(nvme disconnect),  this
will interrupt
error_recovery or reconnect, but ctrl is  freezed and request queue is
quiescing,
so the new IO or timeouted IOs(requeue to hctx->dispatch_list) cannot continue
to process, as a result, nvme_remove_namespaces hang on flush scan_work or
blk_mq_freeze_queue_wait, new IO hang on __bio_queue_enter(), it seems that
if the first patch of my patchset add the next code, it may cover Ming's case:

static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl)
{
    /* If we are resetting/deleting then do nothing */
    if (ctrl->state != NVME_CTRL_CONNECTING) {
        WARN_ON_ONCE(ctrl->state == NVME_CTRL_NEW ||
        ctrl->state == NVME_CTRL_LIVE);
        return;
    }

    if (nvmf_should_reconnect(ctrl)) {
        dev_info(ctrl->device, "Reconnecting in %d seconds...\n",
            ctrl->opts->reconnect_delay);
        queue_delayed_work(nvme_wq, &to_tcp_ctrl(ctrl)->connect_work,
            ctrl->opts->reconnect_delay * HZ);
    } else {
        dev_info(ctrl->device, "Removing controller...\n");
+      nvme_ctrl_reconnect_exit(ctrl);
        nvme_delete_ctrl(ctrl);
    }
}

Thanks.

> Looks the same to me.