linux-kernel - Re: [PATCH RFC 06/26] ipc: Replace spin_unlock

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Date:   Sat, 1 Jul 2017 20:16:24 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Manfred Spraul <manfred@...orfullife.com>
Cc:     linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, oleg@...hat.com, akpm@...ux-foundation.org,
        mingo@...hat.com, dave@...olabs.net, 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
Subject: Re: [PATCH RFC 06/26] ipc: Replace spin_unlock_wait() with
 lock/unlock pair

On Sat, Jul 01, 2017 at 09:23:03PM +0200, Manfred Spraul wrote:
> On 06/30/2017 02:01 AM, Paul E. McKenney wrote:
> >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: Manfred Spraul <manfred@...orfullife.com>
> >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>

Applied, thank you!

							Thanx, Paul

> >---
> >  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;
> >  		}
> 
>