rcu: Stop disabling interrupts in scheduler fastpaths

We need the scheduler's fastpaths to be, well, fast, and unnecessarily
disabling and re-enabling interrupts is not necessarily consistent with
this goal.  Especially given that there are regions of the scheduler that
already have interrupts disabled.

This commit therefore moves the call to rcu_note_context_switch()
to one of the interrupts-disabled regions of the scheduler, and
removes the now-redundant disabling and re-enabling of interrupts from
rcu_note_context_switch() and the functions it calls.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Shift rcu_note_context_switch() to avoid deadlock, as suggested
  by Peter Zijlstra. ]

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 60d15a080d7c..9d3eda39bcd2 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -37,7 +37,7 @@ void rcu_cpu_stall_reset(void);
 /*
  * Note a virtualization-based context switch.  This is simply a
  * wrapper around rcu_note_context_switch(), which allows TINY_RCU
- * to save a few bytes.
+ * to save a few bytes. The caller must have disabled interrupts.
  */
 static inline void rcu_virt_note_context_switch(int cpu)
 {