core: Replace __get_cpu_var with __this_cpu_read if not used for an address.

__get_cpu_var() can be replaced with this_cpu_read and will then use a
single read instruction with implied address calculation to access the
correct per cpu instance.

However, the address of a per cpu variable passed to __this_cpu_read()
cannot be determined (since it's an implied address conversion through
segment prefixes).  Therefore apply this only to uses of __get_cpu_var
where the address of the variable is not used.

Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Hugh Dickins <hughd@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ccdc04c47981..aeebf772d6a2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -367,8 +367,8 @@ void rcu_irq_exit(void)
         WARN_ON_ONCE(rdtp->dynticks & 0x1);
 
         /* If the interrupt queued a callback, get out of dyntick mode. */
-        if (__get_cpu_var(rcu_sched_data).nxtlist ||
-            __get_cpu_var(rcu_bh_data).nxtlist)
+        if (__this_cpu_read(rcu_sched_data.nxtlist) ||
+            __this_cpu_read(rcu_bh_data.nxtlist))
                 set_need_resched();
 }