netdev - Re: [PATCH] net: fix race in the receive/select

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Date:	Fri, 26 Jun 2009 15:46:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Jiri Olsa <jolsa@...hat.com>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	fbl@...hat.com, nhorman@...hat.com, davem@...hat.com,
	Tejun Heo <htejun@...il.com>
Subject: Re: [PATCH] net: fix race in the receive/select

On 06/26, Eric Dumazet wrote:
>
> Davide Libenzi a écrit :
> >
> > Do you think of it as good design adding an MB on a subsystem, because of
> > the special locking logic of another one?
> > The (eventual) slowdown, IMO can be argued sideways, by saying that
> > non-socket users will pay the price for their polls.
>
> I wont argue with you David, just try to correct bugs.

I must admit, I agree with David.

> fs/ext4/ioctl.c line 182
>
> 	set_current_state(TASK_INTERRUPTIBLE);
> 	add_wait_queue(&EXT4_SB(sb)->ro_wait_queue, &wait);
> 	if (timer_pending(&EXT4_SB(sb)->turn_ro_timer)) {
> 		schedule();
>
> Another example of missing barrier after add_wait_queue()

Assuming that ->turn_ro_timer does wake_up(->ro_wait_queue) everything
is OK, we do not need a barrier.

Oleg.

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