From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: manfred@colorfullife.com, Waiman.Long@hpe.com, mingo@kernel.org,
torvalds@linux-foundation.org, ggherdovich@suse.com,
mgorman@techsingularity.net, linux-kernel@vger.kernel.org,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Will Deacon <will.deacon@arm.com>
Subject: Re: sem_lock() vs qspinlocks
Date: Fri, 20 May 2016 09:20:40 -0700 [thread overview]
Message-ID: <20160520162040.GD7086@linux-uzut.site> (raw)
In-Reply-To: <20160520115819.GF3193@twins.programming.kicks-ass.net>
On Fri, 20 May 2016, Peter Zijlstra wrote:
>The problem is that the clear_pending_set_locked() is an unordered
>store, therefore this store can be delayed until no later than
>spin_unlock() (which orders against it due to the address dependency).
>
>This opens numerous races; for example:
>
> ipc_lock_object(&sma->sem_perm);
> sem_wait_array(sma);
>
> false -> spin_is_locked(&sma->sem_perm.lock)
>
>is entirely possible, because sem_wait_array() consists of pure reads,
>so the store can pass all that, even on x86.
I had pondered at the unordered stores in clear_pending_set_locked() for arm,
for example, but I _certainly_ missed this for x86 inside the ACQUIRE region.
Thanks,
Davidlohr
next prev parent reply other threads:[~2016-05-20 16:21 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-20 5:39 sem_lock() vs qspinlocks Davidlohr Bueso
2016-05-20 7:49 ` Peter Zijlstra
2016-05-20 15:00 ` Davidlohr Bueso
2016-05-20 15:05 ` Peter Zijlstra
2016-05-20 15:25 ` Davidlohr Bueso
2016-05-20 15:28 ` Peter Zijlstra
2016-05-20 20:47 ` Waiman Long
2016-05-20 20:52 ` Peter Zijlstra
2016-05-21 0:59 ` Davidlohr Bueso
2016-05-21 4:01 ` Waiman Long
2016-05-21 7:40 ` Peter Zijlstra
2016-05-20 7:53 ` Peter Zijlstra
2016-05-20 8:13 ` Peter Zijlstra
2016-05-20 8:18 ` Peter Zijlstra
2016-05-20 9:07 ` Giovanni Gherdovich
2016-05-20 9:34 ` Peter Zijlstra
2016-05-20 8:30 ` Peter Zijlstra
2016-05-20 9:00 ` Peter Zijlstra
2016-05-20 10:09 ` Ingo Molnar
2016-05-20 10:45 ` Mel Gorman
2016-05-20 11:58 ` Peter Zijlstra
2016-05-20 14:05 ` Boqun Feng
2016-05-20 15:21 ` Peter Zijlstra
2016-05-20 16:04 ` Peter Zijlstra
2016-05-20 17:00 ` Linus Torvalds
2016-05-20 21:06 ` Peter Zijlstra
2016-05-20 21:44 ` Linus Torvalds
2016-05-21 0:48 ` Davidlohr Bueso
2016-05-21 2:30 ` Linus Torvalds
2016-05-21 7:37 ` Peter Zijlstra
2016-05-21 13:49 ` Manfred Spraul
2016-05-24 10:57 ` Peter Zijlstra
2016-05-21 17:14 ` Davidlohr Bueso
2016-05-23 12:25 ` Peter Zijlstra
2016-05-23 17:52 ` Linus Torvalds
2016-05-25 6:37 ` Boqun Feng
2016-05-22 8:43 ` Manfred Spraul
2016-05-22 9:38 ` Peter Zijlstra
2016-05-20 16:20 ` Davidlohr Bueso [this message]
2016-05-20 20:44 ` Waiman Long
2016-05-20 20:53 ` Peter Zijlstra
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