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

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Date:	Thu, 24 Mar 2011 00:13:46 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	shemminger@...tta.com, fchecconi@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net_sched: fix THROTTLED/RUNNING race

From: Eric Dumazet <eric.dumazet@...il.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@...il.com>

Applied, thanks a lot for tracking this down Eric.
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