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

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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@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/exit.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index c5548faa9f37..abfbcf66e5c0 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -819,7 +819,8 @@ 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",
-- 
2.5.2

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[PATCH tip/core/rcu 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 3/9] sched: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 5/9] exit: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 2/9] task_work: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 8/9] locking: Remove spin_unlock_wait() generic definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 7/9] drivers/ata: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 9/9] arch: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 6/9] ipc: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200
  [PATCH tip/core/rcu 4/9] completion: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:20 +0200

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