From: Davidlohr Bueso <dave@stgolabs.net>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-next@vger.kernel.org, 1vier1@web.de,
felixh@informatik.uni-bremen.de, stable@vger.kernel.org
Subject: Re: [PATCH 1/2] ipc/sem.c: Fix complex_count vs. simple op race
Date: Fri, 1 Jul 2016 09:52:58 -0700 [thread overview]
Message-ID: <20160701165258.GA27566@linux-80c1.suse> (raw)
In-Reply-To: <ac93292c-c995-9c05-9e97-06c19ea7a2bf@colorfullife.com>
On Thu, 30 Jun 2016, Manfred Spraul wrote:
>On 06/28/2016 07:27 AM, Davidlohr Bueso wrote:
>If I understand it right, it means that spin_lock() is both an acquire
>and a release - for qspinlocks.
I wouldn't say that: the _Q_LOCKED_VAL stores are still unordered inside
the acquire region but no further than the the unlock store-release; which
is fine for regular mutual exclusion.
>It this valid for all spinlock implementations, for all architectures?
>Otherwise: How can I detect in generic code if I can rely on a release
>inside spin_lock()?
With ticket locks this was never an issue as special lock readers
(spin_unlock_wait(), spin_is_locked()) will always see the lock taken as
they observe waiters by adding itself to the tail -- something the above
commit mimics and piggy backs on to save expensive smp_rmb().
In addition, see 726328d92a4 (locking/spinlock, arch: Update and fix
spin_unlock_wait() implementations).
Thanks,
Davidlohr
next prev parent reply other threads:[~2016-07-01 16:53 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-15 5:23 linux-next: manual merge of the akpm-current tree with the tip tree Stephen Rothwell
2016-06-18 19:39 ` Manfred Spraul
2016-06-18 20:02 ` [PATCH 1/2] ipc/sem.c: Fix complex_count vs. simple op race Manfred Spraul
2016-06-18 20:02 ` Manfred Spraul
2016-06-18 20:02 ` [PATCH 2/2] ipc/sem: sem_lock with hysteresis Manfred Spraul
2016-06-21 20:29 ` Davidlohr Bueso
2016-06-25 17:37 ` Manfred Spraul
2016-06-28 17:54 ` Davidlohr Bueso
2016-06-20 23:04 ` [PATCH 1/2] ipc/sem.c: Fix complex_count vs. simple op race Andrew Morton
2016-06-20 23:04 ` Andrew Morton
2016-06-23 18:55 ` Manfred Spraul
2016-06-21 0:30 ` Davidlohr Bueso
2016-06-23 19:22 ` Manfred Spraul
2016-06-28 5:27 ` Davidlohr Bueso
2016-06-30 19:28 ` Manfred Spraul
2016-07-01 16:52 ` Davidlohr Bueso [this message]
-- strict thread matches above, loose matches on Subject: below --
2016-06-25 17:37 [PATCH 0/2] ipc/sem.c: sem_lock fixes Manfred Spraul
2016-06-25 17:37 ` [PATCH 1/2] ipc/sem.c: Fix complex_count vs. simple op race Manfred Spraul
2016-06-25 19:41 ` Holger Hoffstätte
2016-07-13 5:06 [PATCH 0/2] ipc/sem.c: sem_lock fixes Manfred Spraul
2016-07-13 5:06 ` [PATCH 1/2] ipc/sem.c: Fix complex_count vs. simple op race Manfred Spraul
2016-07-16 1:27 ` Davidlohr Bueso
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