rcu: Avoid misordering in __call_rcu_nocb_enqueue()
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tue, 12 Aug 2014 17:47:48 +0000 (10:47 -0700)
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tue, 16 Sep 2014 17:08:03 +0000 (10:08 -0700)
commit39953dfd40077c7480b1d5deb4d617e086b1c865
tree5839c9da287c82a7c7103199a3b793ecb5391f2f
parent663e131090dd10bac9dc0b4f5b624dd3211b20f6
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>
kernel/rcu/tree_plugin.h