From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de,
Waiman.Long@hpe.com, jason.low2@hp.com,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 1/4] locking/rwsem: Avoid stale ->count for rwsem_down_write_failed()
Date: Mon, 9 May 2016 07:29:23 -0700 [thread overview]
Message-ID: <20160509142923.GA29630@linux-uzut.site> (raw)
In-Reply-To: <573021D5.4070406@hurleysoftware.com>
On Sun, 08 May 2016, Peter Hurley wrote:
>On 05/08/2016 09:56 PM, Davidlohr Bueso wrote:
>> The field is obviously updated w.o the lock and needs a READ_ONCE
>> while waiting for lock holder(s) to go away, just like we do with
>> all other ->count accesses.
>
>This isn't actually fixing a bug because it's passed through
>several full barriers which will force reloading from sem->count.
Yes.
>
>I think the patch is ok if you want it just for consistency anyway,
>but please change $subject and changelog.
Yeah, I wasn't actually concerned about a specific bug, it was more
just for documentation and consistency. This code has been like this
for ever, but it would still be good to have the READ_ONCE. It is
slightly suboptimal to use, but I do not see any real impact either.
Thanks,
Davidlohr
next prev parent reply other threads:[~2016-05-09 14:30 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-09 4:56 [PATCH -tip 0/4] locking/rwsem (xadd): Reader waiter optimizations Davidlohr Bueso
2016-05-09 4:56 ` [PATCH 1/4] locking/rwsem: Avoid stale ->count for rwsem_down_write_failed() Davidlohr Bueso
2016-05-09 5:36 ` Peter Hurley
2016-05-09 7:12 ` Peter Zijlstra
2016-05-09 14:29 ` Davidlohr Bueso [this message]
2016-05-09 4:56 ` [PATCH 2/4] locking/rwsem: Drop superfluous waiter refcount Davidlohr Bueso
2016-05-09 7:39 ` Peter Zijlstra
2016-05-09 15:56 ` Davidlohr Bueso
2016-05-09 16:11 ` Peter Zijlstra
2016-05-09 18:51 ` Davidlohr Bueso
2016-05-09 18:59 ` Peter Zijlstra
2016-05-09 4:56 ` [PATCH 3/4] locking/rwsem: Enable lockless waiter wakeup(s) Davidlohr Bueso
2016-05-09 7:48 ` Peter Zijlstra
2016-05-09 4:56 ` [PATCH 4/4] locking/rwsem: Rework zeroing reader waiter->task Davidlohr Bueso
2016-05-09 7:50 ` Peter Zijlstra
2016-05-10 1:31 ` [PATCH -tip 0/4] locking/rwsem (xadd): Reader waiter optimizations Waiman Long
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