Re: [PATCH] net_sched: fix THROTTLED/RUNNING race

David Miller
2011-03-24T07:13:08Z

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 24 Mar 2011 07:53:57 +0100

> [PATCH] net_sched: fix THROTTLED/RUNNING race
>
> commit fd245a4adb52 (net_sched: move TCQ_F_THROTTLED flag)
> added a race.
>
> qdisc_watchdog() is run from softirq, so special care should be taken or
> we can lose one state transition (THROTTLED/RUNNING)
>
> Prior to fd245a4adb52, we were manipulating q->flags (qdisc->flags &=
> ~TCQ_F_THROTTLED;) and this manipulation could only race with
> qdisc_warn_nonwc().
>
> Since we want to avoid atomic ops in qdisc fast path - it was the
> meaning of commit 371121057607e (QDISC_STATE_RUNNING dont need atomic
> bit ops) - fix is to move THROTTLE bit into 'state' field, this one
> being manipulated with SMP and IRQ safe operations.
>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>

Applied, thanks a lot for tracking this down Eric.