netdev - [PATCH RFC 03/26] sched: Replace spin_unlock

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Message-Id: <1498780894-8253-3-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Thu, 29 Jun 2017 17:01:11 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        oleg@...hat.com, akpm@...ux-foundation.org, mingo@...hat.com,
        dave@...olabs.net, manfred@...orfullife.com, tj@...nel.org,
        arnd@...db.de, linux-arch@...r.kernel.org, will.deacon@....com,
        peterz@...radead.org, stern@...land.harvard.edu,
        parri.andrea@...il.com, torvalds@...ux-foundation.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC 03/26] sched: Replace spin_unlock_wait() with lock/unlock pair

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_task_dead() with spin_lock() followed immediately by spin_unlock().
This should be safe from a performance perspective because the lock is
this tasks ->pi_lock, and this is called only after the task exits.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will.deacon@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Andrea Parri <parri.andrea@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
 kernel/sched/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e91138fcde86..6dea3d9728c8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3461,7 +3461,8 @@ void __noreturn do_task_dead(void)
 	 * is held by try_to_wake_up()
 	 */
 	smp_mb();
-	raw_spin_unlock_wait(&current->pi_lock);
+	raw_spin_lock(&current->pi_lock);
+	raw_spin_unlock(&current->pi_lock);
 
 	/* Causes final put_task_struct in finish_task_switch(): */
 	__set_current_state(TASK_DEAD);
-- 
2.5.2