From: Andrew Morton <akpm@linux-foundation.org>
To: Davidlohr Bueso <davidlohr.bueso@hp.com>,
Emmanuel Benisty <benisty.e@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Rik van Riel <riel@surriel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
hhuang@redhat.com, "Low, Jason" <jason.low2@hp.com>,
Michel Lespinasse <walken@google.com>,
Larry Woodman <lwoodman@redhat.com>,
"Vinod, Chegu" <chegu_vinod@hp.com>
Subject: Re: ipc,sem: sysv semaphore scalability
Date: Tue, 16 Apr 2013 16:30:41 -0700 [thread overview]
Message-ID: <20130416163041.dfa3e82bfa6b10ae8ffe7608@linux-foundation.org> (raw)
In-Reply-To: <20130326113533.41ad9ee33b2d010b2a83e7c0@linux-foundation.org>
On Tue, 26 Mar 2013 11:35:33 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> Do we need the locking at all? What does it actually do?
>
> sem_lock_and_putref(sma);
> if (sma->sem_perm.deleted) {
> sem_unlock(sma, -1);
> err = -EIDRM;
> goto out_free;
> }
> sem_unlock(sma, -1);
>
> We're taking the lock, testing an int and then dropping the lock.
> What's the point in that?
Rikpoke.
The new semctl_main() is now taking a lock, testing
sma->sem_perm.deleted then dropping that lock. It looks wrong. What
is that lock testing against? What prevents .deleted from changing
value 1ns after we dropped that lock?
next prev parent reply other threads:[~2013-04-16 23:30 UTC|newest]
Thread overview: 129+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-20 19:55 ipc,sem: sysv semaphore scalability Rik van Riel
2013-03-20 19:55 ` [PATCH 1/7] ipc: remove bogus lock comment for ipc_checkid Rik van Riel
2013-03-20 19:55 ` [PATCH 2/7] ipc: introduce obtaining a lockless ipc object Rik van Riel
2013-03-20 19:55 ` [PATCH 3/7] ipc: introduce lockless pre_down ipcctl Rik van Riel
2013-03-20 19:55 ` [PATCH 4/7] ipc,sem: do not hold ipc lock more than necessary Rik van Riel
2013-03-20 19:55 ` [PATCH 5/7] ipc,sem: open code and rename sem_lock Rik van Riel
2013-03-22 1:14 ` Davidlohr Bueso
2013-03-20 19:55 ` [PATCH 6/7] ipc,sem: have only one list in struct sem_queue Rik van Riel
2013-03-22 1:14 ` Davidlohr Bueso
2013-03-20 19:55 ` [PATCH 7/7] ipc,sem: fine grained locking for semtimedop Rik van Riel
2013-03-22 1:14 ` Davidlohr Bueso
2013-03-22 23:01 ` Michel Lespinasse
2013-03-22 23:38 ` Rik van Riel
2013-03-22 23:42 ` [PATCH 7/7 part3] fix for sem_lock Rik van Riel
2013-03-20 20:49 ` ipc,sem: sysv semaphore scalability Linus Torvalds
2013-03-20 20:56 ` Linus Torvalds
2013-03-20 20:57 ` Davidlohr Bueso
2013-03-21 21:10 ` Andrew Morton
2013-03-21 21:47 ` Peter Hurley
2013-03-21 21:50 ` Peter Hurley
2013-03-21 22:01 ` Andrew Morton
2013-03-22 3:38 ` Rik van Riel
2013-03-26 19:28 ` Dave Jones
2013-03-26 19:43 ` Andrew Morton
2013-03-29 16:17 ` Dave Jones
2013-03-29 18:00 ` Linus Torvalds
2013-03-29 18:04 ` Dave Jones
2013-03-29 18:10 ` Linus Torvalds
2013-03-29 18:43 ` Linus Torvalds
2013-03-29 19:06 ` Dave Jones
2013-03-29 19:13 ` Linus Torvalds
2013-03-29 19:26 ` Linus Torvalds
2013-03-29 19:36 ` Peter Hurley
2013-04-02 16:08 ` Sasha Levin
2013-04-02 17:24 ` Linus Torvalds
2013-04-02 17:52 ` Linus Torvalds
2013-04-02 19:53 ` Sasha Levin
2013-04-02 20:00 ` Dave Jones
2013-03-29 19:33 ` Peter Hurley
2013-03-29 19:54 ` Linus Torvalds
2013-04-01 7:40 ` Stanislav Kinsbursky
2013-03-29 20:41 ` Linus Torvalds
2013-03-29 21:12 ` Linus Torvalds
2013-03-29 23:16 ` Linus Torvalds
2013-03-30 1:36 ` Emmanuel Benisty
2013-03-30 2:08 ` Davidlohr Bueso
2013-03-30 3:02 ` Emmanuel Benisty
2013-03-30 3:46 ` Linus Torvalds
2013-03-30 4:33 ` Emmanuel Benisty
2013-03-30 5:10 ` Linus Torvalds
2013-03-30 5:57 ` Emmanuel Benisty
2013-03-30 17:22 ` Linus Torvalds
2013-03-31 2:38 ` Emmanuel Benisty
2013-03-31 5:01 ` Davidlohr Bueso
2013-03-31 13:45 ` Rik van Riel
2013-03-31 17:10 ` Linus Torvalds
2013-03-31 17:02 ` Emmanuel Benisty
2013-03-30 2:09 ` Linus Torvalds
2013-03-30 2:55 ` Davidlohr Bueso
2013-03-29 19:01 ` Dave Jones
2013-05-03 15:03 ` Peter Hurley
2013-03-22 1:12 ` Davidlohr Bueso
2013-03-22 1:23 ` Linus Torvalds
2013-03-22 3:40 ` Rik van Riel
2013-03-22 7:30 ` Mike Galbraith
2013-03-22 11:04 ` Emmanuel Benisty
2013-03-22 15:37 ` Linus Torvalds
2013-03-23 3:19 ` Emmanuel Benisty
2013-03-23 19:45 ` Linus Torvalds
2013-03-24 13:46 ` Emmanuel Benisty
2013-03-24 17:10 ` Linus Torvalds
2013-03-25 13:47 ` Emmanuel Benisty
2013-03-25 14:00 ` Rik van Riel
2013-03-25 14:03 ` Rik van Riel
2013-03-25 15:20 ` Emmanuel Benisty
2013-03-25 15:53 ` Rik van Riel
2013-03-25 17:09 ` Emmanuel Benisty
2013-03-25 14:01 ` Rik van Riel
2013-03-25 14:21 ` Emmanuel Benisty
2013-03-26 17:59 ` Davidlohr Bueso
2013-03-26 18:14 ` Rik van Riel
2013-03-26 18:35 ` Andrew Morton
2013-04-16 23:30 ` Andrew Morton [this message]
2013-05-04 15:55 ` Jörn Engel
2013-05-04 18:12 ` Borislav Petkov
2013-05-06 14:47 ` Jörn Engel
2013-03-22 17:51 ` Davidlohr Bueso
2013-03-25 20:21 ` Sasha Levin
2013-03-25 20:38 ` [PATCH -mm -next] ipc,sem: fix lockdep false positive Rik van Riel
2013-03-25 21:42 ` Michel Lespinasse
2013-03-25 21:51 ` Michel Lespinasse
2013-03-25 21:56 ` Sasha Levin
2013-03-25 21:52 ` Sasha Levin
2013-03-26 13:19 ` Peter Zijlstra
2013-03-26 13:40 ` Michel Lespinasse
2013-03-26 14:27 ` Peter Zijlstra
2013-03-26 15:19 ` Rik van Riel
2013-03-27 8:40 ` Peter Zijlstra
2013-03-27 8:42 ` Peter Zijlstra
2013-03-27 11:22 ` Michel Lespinasse
2013-03-27 12:02 ` Peter Zijlstra
2013-03-27 20:00 ` Rik van Riel
2013-03-28 20:23 ` [PATCH v2 " Rik van Riel
2013-03-29 2:50 ` Michel Lespinasse
2013-03-29 9:57 ` Peter Zijlstra
2013-03-29 13:21 ` Michel Lespinasse
2013-03-29 12:07 ` Rik van Riel
2013-03-29 13:08 ` Michel Lespinasse
2013-03-29 13:24 ` Rik van Riel
2013-03-29 13:55 ` [PATCH v3 " Rik van Riel
2013-03-29 13:59 ` Michel Lespinasse
2013-03-26 14:25 ` [PATCH " Rik van Riel
2013-03-26 17:33 ` ipc,sem: sysv semaphore scalability Sasha Levin
2013-03-26 17:51 ` Davidlohr Bueso
2013-03-26 18:07 ` Sasha Levin
2013-03-26 18:17 ` Rik van Riel
2013-03-26 20:00 ` [PATCH -mm -next] ipc,sem: untangle RCU locking with find_alloc_undo Rik van Riel
2013-04-05 4:38 ` Mike Galbraith
2013-04-05 13:21 ` Rik van Riel
2013-04-05 16:26 ` Mike Galbraith
2013-04-16 12:37 ` Mike Galbraith
2013-03-26 17:55 ` ipc,sem: sysv semaphore scalability Paul E. McKenney
2013-03-28 15:32 ` [PATCH -mm -next] ipc,sem: untangle RCU locking with find_alloc_undo Rik van Riel
2013-03-28 21:05 ` Davidlohr Bueso
2013-03-29 1:00 ` Michel Lespinasse
2013-03-29 1:14 ` Sasha Levin
2013-03-30 13:35 ` Sasha Levin
2013-03-31 1:30 ` Rik van Riel
2013-03-31 4:09 ` Davidlohr Bueso
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