From: Tom Herbert <tom@herbertland.com>
Date: Wed, 5 Aug 2015 16:39:27 +0000 (-0700)
Subject: net: Fix race condition in store_rps_map
X-Git-Tag: omap-for-v4.3/fixes-rc1~110^2~214
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=10e4ea751;p=pandora-kernel.git

net: Fix race condition in store_rps_map

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@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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