netdev - Re: [PATCH net 0/3] Fix Qdisc destroy issues caused by adding fine-grained locking to filter API

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Date:   Wed, 18 Sep 2019 15:50:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net 0/3] Fix Qdisc destroy issues caused by adding
 fine-grained locking to filter API

On Wed, Sep 18, 2019 at 12:32 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
> TC filter API unlocking introduced several new fine-grained locks. The
> change caused sleeping-while-atomic BUGs in several Qdiscs that call cls
> APIs which need to obtain new mutex while holding sch tree spinlock. This
> series fixes affected Qdiscs by ensuring that cls API that became sleeping
> is only called outside of sch tree lock critical section.

Sorry I just took a deeper look. It seems harder than just moving it
out of the critical section.

qdisc_destroy() calls ops->reset() which usually purges queues,
I don't see how it is safe to move it out of tree spinlock without
respecting fast path.

What do you think?