netdev - Re: [PATCH net] net: sch_red: Fix race between timer and red

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Message-Id: <20131105.221633.636594084725891709.davem@davemloft.net>
Date:	Tue, 05 Nov 2013 22:16:33 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	subramanian.vijay@...il.com
Cc:	netdev@...r.kernel.org, shemminger@...tta.com,
	eric.dumazet@...il.com
Subject: Re: [PATCH net] net: sch_red: Fix race between timer and
 red_destroy()

From: Vijay Subramanian <subramanian.vijay@...il.com>
Date: Mon,  4 Nov 2013 18:08:16 -0800

> Make sure timer does not fire once qdisc is destroyed.
> 
> Signed-off-by: Vijay Subramanian <subramanian.vijay@...il.com>

I do not understand how this problem can trigger.

del_timer_sync() waits for all instances of the timer handler which
are running to complete, and then it deletes the timer from any of
the scheduled timer lists.

Your patch is making the mod_timer() in the timer handler conditional,
and this really shouldn't be necessary.

The whole point of del_timer_sync() is to address these kinds of
situations.
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