From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Tue, 12 Aug 2014 17:47:48 +0000 (-0700)
Subject: rcu: Avoid misordering in __call_rcu_nocb_enqueue()
X-Git-Tag: fixes-against-v3.18-rc2~103^2~1^2~16^3~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=39953dfd40077c7480b1d5deb4d617e086b1c865;p=pandora-kernel.git

rcu: Avoid misordering in __call_rcu_nocb_enqueue()

The NOCB leader wakeup ordering depends on the store to the header
happening before the check for the leader already being awake.  However,
because atomic_long_add() does not return a value, it does not provide
ordering guarantees, the incorrect comment in wake_nocb_leader()
notwithstanding.  This commit therefore adds a smp_mb__after_atomic()
after the final atomic_long_add() to provide the needed ordering
guarantee.

Reported-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>
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