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From: Cong Wang <xiyou.wangcong@gmail.com>
To: Petr Machata <petrm@mellanox.com>
Cc: Linux Kernel Network Developers <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Jiri Pirko <jiri@mellanox.com>,
	Ido Schimmel <idosch@mellanox.com>
Subject: Re: [PATCH net-next v1 2/5] net: sched: Introduce helpers for qevent blocks
Date: Wed, 8 Jul 2020 12:09:04 -0700	[thread overview]
Message-ID: <CAM_iQpUbPidrm+DucpDO4yTaW=o3Pw=mYNTon9uYi4_O36Aw+A@mail.gmail.com> (raw)
In-Reply-To: <87y2nugepz.fsf@mellanox.com>

On Wed, Jul 8, 2020 at 9:21 AM Petr Machata <petrm@mellanox.com> wrote:
>
> Actually I guess I could qdisc_refcount_inc() the current qdisc so that
> it doesn't go away. Then when enqueing I could access the child
> directly, not relying on the now-obsolete cache from the beginning of
> the enqueue function. I suppose that a similar approach could be used in
> other users of tcf_classify() as well. What do you think?

The above example is just a quick one I can think of, there could be
more race conditions that lead to other kinds of bugs.

I am sure you can fix that one, but the point is that it is hard to
audit and fix them all. The best solution here is of course not to
release that lock, but again it requires some more work to avoid
the deadlock.

Thanks.

  reply	other threads:[~2020-07-08 19:09 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-26 22:45 [PATCH net-next v1 0/5] TC: Introduce qevents Petr Machata
2020-06-26 22:45 ` [PATCH net-next v1 1/5] net: sched: Pass root lock to Qdisc_ops.enqueue Petr Machata
2020-07-06 19:21   ` Cong Wang
2020-07-07 15:25     ` Petr Machata
2020-07-07 19:41       ` Cong Wang
2020-06-26 22:45 ` [PATCH net-next v1 2/5] net: sched: Introduce helpers for qevent blocks Petr Machata
2020-07-06 19:48   ` Cong Wang
2020-07-07 15:22     ` Petr Machata
2020-07-07 19:13       ` Cong Wang
2020-07-08 12:35         ` Petr Machata
2020-07-08 16:21           ` Petr Machata
2020-07-08 19:09             ` Cong Wang [this message]
2020-07-08 19:04           ` Cong Wang
2020-07-08 21:04             ` Petr Machata
2020-07-09  0:13               ` Petr Machata
2020-07-09 19:37                 ` Cong Wang
2020-07-10 14:40                   ` Petr Machata
2020-07-14  2:51                     ` Cong Wang
2020-07-14  9:12                       ` Petr Machata
2020-07-07 19:48   ` Cong Wang
2020-07-08  9:19     ` Petr Machata
2020-06-26 22:45 ` [PATCH net-next v1 3/5] net: sched: sch_red: Split init and change callbacks Petr Machata
2020-06-26 22:45 ` [PATCH net-next v1 4/5] net: sched: sch_red: Add qevents "early_drop" and "mark" Petr Machata
2020-06-26 22:45 ` [PATCH net-next v1 5/5] selftests: forwarding: Add a RED test for SW datapath Petr Machata
2020-06-26 22:45 ` [PATCH iproute2-next v1 1/4] uapi: pkt_sched: Add two new RED attributes Petr Machata
2020-06-26 22:45   ` [PATCH iproute2-next v1 2/4] tc: Add helpers to support qevent handling Petr Machata
2020-06-26 22:45   ` [PATCH iproute2-next v1 3/4] man: tc: Describe qevents Petr Machata
2020-06-26 22:45   ` [PATCH iproute2-next v1 4/4] tc: q_red: Add support for qevents "mark" and "early_drop" Petr Machata
2020-06-26 22:56 ` [PATCH net-next v1 0/5] TC: Introduce qevents Stephen Hemminger
2020-06-29 13:21   ` Petr Machata
2020-06-30  0:15 ` David Miller

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