lockdep WARNING at blktests block/011

[Shinichiro Kawasaki]

On Oct 04, 2022 / 20:10, Tetsuo Handa wrote:
> On 2022/10/04 19:44, Shinichiro Kawasaki wrote:
> > Any comment on this patch will be appreciated. If this action approach is ok,
> > I'll post as a formal patch for review.
> 
> I don't want you to make such change.
> 
> I saw a case where real deadlock was hidden by lockdep_set_novalidate_class().
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=62ebaf2f9261cd2367ae928a39343fcdbfe9f877
>   https://groups.google.com/g/syzkaller-bugs/c/Uj9LqEUCwac/m/BhdTjWhNAQAJ
> 
> In general, this kind of deadlock possibility had better be addressed by bringing
> problematic locks out of cancel{,_delayed}_work_sync() section.
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=a91b750fd6629354460282bbf5146c01b05c4859

Thanks for the comment. Then, I think the question is how to move the
blk_sync_queue() call out of the ctrl->namespaces_rwsem critical section in
nvme_sync_io_queues():

void nvme_sync_io_queues(struct nvme_ctrl *ctrl)
{
	struct nvme_ns *ns;

	down_read(&ctrl->namespaces_rwsem);
	list_for_each_entry(ns, &ctrl->namespaces, list)
		blk_sync_queue(ns->queue);
	up_read(&ctrl->namespaces_rwsem);
}

I'm not yet sure how we can do it. I guess it is needed to copy the
ctrl->namespaces list to a temporary array to refer out of the critical section.
Also need to keep kref of each ns not to free. Will try to implement tomorrow.

-- 
Shin'ichiro Kawasaki