[PATCH v2 5/9] exit: Replace spin_unlock_wait() with lock/unlock pair

From: Paul E. McKenney
Date: Wed Jul 05 2017 - 19:32:58 EST

There is no agreed-upon definition of spin_unlock_wait()'s semantics, and
it appears that all callers could do just as well with a lock/unlock pair.
This commit therefore replaces the spin_unlock_wait() call in do_exit()
with spin_lock() followed immediately by spin_unlock(). This should be
safe from a performance perspective because the lock is a per-task lock,
and this is happening only at task-exit time.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
kernel/exit.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 516acdb0e0ec..6d19c9090d43 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -832,7 +832,8 @@ void __noreturn do_exit(long code)
* Ensure that we must observe the pi_state in exit_mm() ->
* mm_release() -> exit_pi_state_list().
- raw_spin_unlock_wait(&tsk->pi_lock);
+ raw_spin_lock_irq(&tsk->pi_lock);
+ raw_spin_unlock_irq(&tsk->pi_lock);

if (unlikely(in_atomic())) {
pr_info("note: %s[%d] exited with preempt_count %d\n",