linux-kernel - [PATCH v2 6/9] ipc: Replace spin_unlock

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Message-Id: <1499297503-23852-6-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Wed,  5 Jul 2017 16:31:40 -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 v2 6/9] ipc: 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
exit_sem() with spin_lock() followed immediately by spin_unlock().
This should be safe from a performance perspective because exit_sem()
is rarely invoked in production.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Davidlohr Bueso <dave@...olabs.net>
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>
Acked-by: Manfred Spraul <manfred@...orfullife.com>
---
 ipc/sem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 947dc2348271..e88d0749a929 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2096,7 +2096,8 @@ void exit_sem(struct task_struct *tsk)
 			 * possibility where we exit while freeary() didn't
 			 * finish unlocking sem_undo_list.
 			 */
-			spin_unlock_wait(&ulp->lock);
+			spin_lock(&ulp->lock);
+			spin_unlock(&ulp->lock);
 			rcu_read_unlock();
 			break;
 		}
-- 
2.5.2