[PATCH 2/2] nvme-multipath: don't block on blk_queue_enter of the underlying device

[Sagi Grimberg]

> I check it again. I still think the below patch can avoid the bug.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5a6c35f9af416114588298aa7a90b15bbed15a41 

I don't understand what you are saying...

> 
> The process:
> 1.nvme_ns_head_submit_bio call srcu_read_lock(&head->srcu).
> 2.nvme_ns_head_submit_bio will add the bio to current->bio_list instead 
> of waiting for the frozen queue.

Nothing guarantees that you have a bio_list active at any point in time,
in fact for a workload that submits one by one you will always drain
that list directly in the submission...

> 3.nvme_ns_head_submit_bio call srcu_read_unlock(&head->srcu, srcu_idx).
> So nvme_ns_head_submit_bio do not hold head->srcu long when the queue is 
> frozen, can avoid deadlock.
> 
> Sagi, suggest trying this patch.

The above reproduces with the patch applied on upstream nvme code.