netdev - Re: [PATCH net-next] net: Fix race condition in store_rps

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Message-Id: <20150807.155726.1475197462744121004.davem@davemloft.net>
Date:	Fri, 07 Aug 2015 15:57:26 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	tom@...bertland.com
Cc:	netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net-next] net: Fix race condition in store_rps_map

From: Tom Herbert <tom@...bertland.com>
Date: Wed, 5 Aug 2015 09:39:27 -0700

> There is a race condition in store_rps_map that allows jump label
> count in rps_needed to go below zero. This can happen when
> concurrently attempting to set and a clear map.
> 
> Scenario:
> 
> 1. rps_needed count is zero
> 2. New map is assigned by setting thread, but rps_needed count _not_ yet
>    incremented (rps_needed count still zero)
> 2. Map is cleared by second thread, old_map set to that just assigned
> 3. Second thread performs static_key_slow_dec, rps_needed count now goes
>    negative
> 
> Fix is to increment or decrement rps_needed under the spinlock.
> 
> Signed-off-by: Tom Herbert <tom@...bertland.com>

Applied, thanks Tom.
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