From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: tglx@linutronix.de, mingo@kernel.org, bigeasy@linutronix.de,
umgwanakikbuti@gmail.com, paulmck@linux.vnet.ibm.com,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 3/3] rtmutex: Reduce top-waiter blocking on a lock
Date: Mon, 14 Mar 2016 14:23:56 +0100 [thread overview]
Message-ID: <20160314132356.GY6356@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1457461223-4301-4-git-send-email-dave@stgolabs.net>
On Tue, Mar 08, 2016 at 10:20:23AM -0800, Davidlohr Bueso wrote:
> lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
> static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
> {
> return (struct task_struct *)
> - ((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL);
> + ((unsigned long)READ_ONCE(lock->owner) & ~RT_MUTEX_OWNER_MASKALL);
> }
If you READ_ONCE(), you should also WRITE_ONCE(), because while the
write is under the proper locks, our friendly compiler might still
choose to emit the store in a random sequence of byte stores, rendering
our READ_ONCE() pointless.
next prev parent reply other threads:[~2016-03-14 13:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-08 18:20 [PATCH -tip 0/3] locking/rtmutex: Another crack at spin on owner Davidlohr Bueso
2016-03-08 18:20 ` [PATCH 1/3] rtmutex: Delete save_state member of struct rt_mutex Davidlohr Bueso
2016-03-08 18:20 ` [PATCH 2/3] rtmutex: Add rt_mutex_init_waiter helper Davidlohr Bueso
2016-03-14 13:16 ` Peter Zijlstra
2016-03-08 18:20 ` [PATCH 3/3] rtmutex: Reduce top-waiter blocking on a lock Davidlohr Bueso
2016-03-14 13:23 ` Peter Zijlstra [this message]
2016-03-08 22:05 ` [PATCH 4/3] rtmutex: Avoid barrier in rt_mutex_handle_deadlock Davidlohr Bueso
2016-03-14 13:40 ` Peter Zijlstra
2016-03-21 18:16 ` Davidlohr Bueso
2016-03-22 10:21 ` Peter Zijlstra
2016-03-22 11:32 ` Heiko Carstens
2016-03-22 12:20 ` Peter Zijlstra
2016-03-22 13:26 ` Heiko Carstens
2016-03-22 13:55 ` Peter Zijlstra
2016-03-22 14:45 ` Heiko Carstens
2016-03-22 16:41 ` Peter Zijlstra
2016-03-22 21:46 ` Heiko Carstens
2016-03-25 2:30 ` Davidlohr Bueso
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