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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-09-25 20:19:02 -0700
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2017-10-03 10:27:32 -0400
commitf39b536ce9248e9799ff900358d6f073ab2e6c55 (patch)
tree6d6a68a41259843d4d6563a3a97f22219d6d72c4 /kernel/rcu
parent2b0b8499ae75df91455bbeb7491d45affc384fb0 (diff)
downloadlinux-f39b536ce9248e9799ff900358d6f073ab2e6c55.tar.bz2
rcu: Remove extraneous READ_ONCE()s from rcu_irq_{enter,exit}()
The read of ->dynticks_nmi_nesting in rcu_irq_enter() and rcu_irq_exit() is currently protected with READ_ONCE(). However, this protection is unnecessary because (1) ->dynticks_nmi_nesting is updated only by the current CPU, (2) Although NMI handlers can update this field, they reset it back to its old value before return, and (3) Interrupts are disabled, so nothing else can modify it. The value of ->dynticks_nmi_nesting is thus effectively constant, and so no protection is required. This commit therefore removes the READ_ONCE() protection from these two accesses. Link: http://lkml.kernel.org/r/20170926031902.GA2074@linux.vnet.ibm.com Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 63bee8e1b193..c03152f7e458 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -890,7 +890,7 @@ void rcu_irq_exit(void)
rdtp = this_cpu_ptr(&rcu_dynticks);
/* Page faults can happen in NMI handlers, so check... */
- if (READ_ONCE(rdtp->dynticks_nmi_nesting))
+ if (rdtp->dynticks_nmi_nesting)
return;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
@@ -1027,7 +1027,7 @@ void rcu_irq_enter(void)
rdtp = this_cpu_ptr(&rcu_dynticks);
/* Page faults can happen in NMI handlers, so check... */
- if (READ_ONCE(rdtp->dynticks_nmi_nesting))
+ if (rdtp->dynticks_nmi_nesting)
return;
oldval = rdtp->dynticks_nesting;