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

[Ming Lei]

Hello Chunguang,

On Mon, May 29, 2023 at 06:59:22PM +0800, brookxu.cn wrote:
> 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

I didn't dig into ctrl state check in these error handler yet, but error
handling is supposed to provide forward progress for any controller state.

Can you explain a bit how switching to DELETING interrupts the above
error handling and breaks the forward progress guarantee?

> 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.

Yeah, nvme freeze usage is fragile, and I suggested to move
nvme_start_freeze() from nvme_tcp_teardown_io_queues to
nvme_tcp_configure_io_queues(), such as the posted change on rdma:

https://lore.kernel.org/linux-block/CAHj4cs-4gQHnp5aiekvJmb6o8qAcb6nLV61uOGFiisCzM49_dg@xxxxxxxxxxxxxx/T/#ma0d6bbfaa0c8c1be79738ff86a2fdcf7582e06b0

> 2. Since queus is quiescing, requeue timeouted IO may hang in hctx->dispatch
>    queue, leading scan_work waiting for IO completion.

That still looks one problem in related error handling code, which is
supposed to recover and unquiesce queue finally.


Thanks, 
Ming