netdev - Re: [net-next PATCH] bpf: cpumap fix potential lost wake-up problem

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Message-Id: <20171024.184048.1933890434085798489.davem@davemloft.net>
Date:   Tue, 24 Oct 2017 18:40:48 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     brouer@...hat.com
Cc:     netdev@...r.kernel.org, mst@...hat.com, riel@...hat.com,
        borkmann@...earbox.net, alexei.starovoitov@...il.com
Subject: Re: [net-next PATCH] bpf: cpumap fix potential lost wake-up problem

From: Jesper Dangaard Brouer <brouer@...hat.com>
Date: Mon, 23 Oct 2017 19:39:28 +0200

> As pointed out by Michael, commit 1c601d829ab0 ("bpf: cpumap xdp_buff
> to skb conversion and allocation") contains a classical example of the
> potential lost wake-up problem.
> 
> We need to recheck the condition __ptr_ring_empty() after changing
> current->state to TASK_INTERRUPTIBLE, this avoids a race between
> wake_up_process() and schedule(). After this, a race with
> wake_up_process() will simply change the state to TASK_RUNNING, and
> the schedule() call not really put us to sleep.
> 
> Fixes: 1c601d829ab0 ("bpf: cpumap xdp_buff to skb conversion and allocation")
> Reported-by: "Michael S. Tsirkin" <mst@...hat.com>

Applied.