From: Oleg Nesterov <oleg@redhat.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, linux-kernel@vger.kernel.org,
paulmck@linux.vnet.ibm.com, corbet@lwn.net, mhocko@kernel.org,
dhowells@redhat.com, torvalds@linux-foundation.org,
will.deacon@arm.com, Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()
Date: Thu, 12 Nov 2015 19:38:07 +0100 [thread overview]
Message-ID: <20151112183807.GA7538@redhat.com> (raw)
In-Reply-To: <20151112151839.GE6314@fixme-laptop.cn.ibm.com>
On 11/12, Boqun Feng wrote:
>
> On Thu, Nov 12, 2015 at 04:00:58PM +0100, Oleg Nesterov wrote:
> >
> > No?
> >
>
> do_exit() is surely buggy if spin_lock() could work in this way.
OK, good ;) so we need to fix spin_lock() on PPC ? Or add
mb__after_unlock_lock() but this leads to other questions... Or
change do_exit() to do lock() + unlock().
>
> > And smp_mb__before_spinlock() looks wrong too then.
> >
>
> Maybe not? As smp_mb__before_spinlock() is used before a LOCK operation,
> which has both LOAD part and STORE part unlike spin_unlock_wait()?
Maybe not.
But let me remind that the original purpose of this mb__before_spinlock()
was to ensure that "CONDITION = true" before ttwu() can not be reordered
with
if (!(p->state & state))
goto out; // do not wakeup
inside try_to_wake_up(). Otherwise
CONDITION = true;
try_to_wake_up(p);
can race with "p" doing
set_current_state(...); // implies mb();
if (CONDITION)
return;
schedule();
because try_to_wake_up() can read p->state before it sets CONDITION = 1
and then it won't wakeup "p" which has already checked this CONDITION.
Now. If try_to_wake_up() can read p->state before it writes to *pi_lock,
then how smp_mb__before_spinlock() == wmb() can help to serialize STORE
and LOAD?
It seems that PPC needs to define smp_mb__before_spinlock() as full mb(),
no?
Oleg.
next prev parent reply other threads:[~2015-11-12 17:42 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-02 13:29 [PATCH 0/4] scheduler ordering bits Peter Zijlstra
2015-11-02 13:29 ` [PATCH 1/4] sched: Better document the try_to_wake_up() barriers Peter Zijlstra
2015-12-04 0:09 ` Byungchul Park
2015-12-04 0:58 ` Byungchul Park
2015-11-02 13:29 ` [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra
2015-11-02 20:27 ` Paul Turner
2015-11-02 20:34 ` Peter Zijlstra
2015-11-02 22:09 ` Paul Turner
2015-11-02 22:12 ` Peter Zijlstra
2015-11-20 10:02 ` Peter Zijlstra
2015-11-20 14:08 ` Boqun Feng
2015-11-20 14:18 ` Peter Zijlstra
2015-11-20 14:21 ` Boqun Feng
2015-11-20 19:41 ` Peter Zijlstra
2015-11-02 13:29 ` [PATCH 3/4] sched: Fix a race in try_to_wake_up() vs schedule() Peter Zijlstra
2015-11-02 13:29 ` [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra
2015-11-02 13:57 ` Peter Zijlstra
2015-11-02 17:43 ` Will Deacon
2015-11-03 1:14 ` Paul E. McKenney
2015-11-03 1:25 ` Linus Torvalds
2015-11-02 17:42 ` Will Deacon
2015-11-02 18:08 ` Linus Torvalds
2015-11-02 18:37 ` Will Deacon
2015-11-02 19:17 ` Linus Torvalds
2015-11-02 19:57 ` Will Deacon
2015-11-02 20:23 ` Peter Zijlstra
2015-11-02 21:56 ` Peter Zijlstra
2015-11-03 1:57 ` Paul E. McKenney
2015-11-03 19:40 ` Linus Torvalds
2015-11-04 3:57 ` Paul E. McKenney
2015-11-04 4:43 ` Linus Torvalds
2015-11-04 12:54 ` Paul E. McKenney
2015-11-02 20:36 ` David Howells
2015-11-02 20:40 ` Peter Zijlstra
2015-11-02 21:11 ` Linus Torvalds
2015-11-03 17:59 ` Oleg Nesterov
2015-11-03 18:23 ` Peter Zijlstra
2015-11-11 9:39 ` Boqun Feng
2015-11-11 10:34 ` Boqun Feng
2015-11-11 19:53 ` Oleg Nesterov
2015-11-12 13:50 ` Paul E. McKenney
2015-11-11 12:12 ` Peter Zijlstra
2015-11-11 19:39 ` Oleg Nesterov
2015-11-11 21:23 ` Linus Torvalds
2015-11-12 7:14 ` Boqun Feng
2015-11-12 10:28 ` Peter Zijlstra
2015-11-12 15:00 ` Oleg Nesterov
2015-11-12 14:40 ` Paul E. McKenney
2015-11-12 14:49 ` Boqun Feng
2015-11-12 15:02 ` Paul E. McKenney
2015-11-12 21:53 ` Will Deacon
2015-11-12 14:50 ` Peter Zijlstra
2015-11-12 15:01 ` Paul E. McKenney
2015-11-12 15:08 ` Peter Zijlstra
2015-11-12 15:20 ` Paul E. McKenney
2015-11-12 21:25 ` Will Deacon
2015-11-12 15:18 ` Boqun Feng
2015-11-12 18:38 ` Oleg Nesterov [this message]
2015-11-12 18:02 ` Peter Zijlstra
2015-11-12 19:33 ` Oleg Nesterov
2015-11-12 18:59 ` Paul E. McKenney
2015-11-12 21:33 ` Will Deacon
2015-11-12 23:43 ` Paul E. McKenney
2015-11-16 13:58 ` Will Deacon
2015-11-12 18:21 ` Linus Torvalds
2015-11-12 22:09 ` Will Deacon
2015-11-16 15:56 ` Peter Zijlstra
2015-11-16 16:04 ` Peter Zijlstra
2015-11-16 16:24 ` Will Deacon
2015-11-16 16:44 ` Paul E. McKenney
2015-11-16 16:46 ` Will Deacon
2015-11-16 17:15 ` Paul E. McKenney
2015-11-16 21:58 ` Linus Torvalds
2015-11-17 11:51 ` Will Deacon
2015-11-17 21:01 ` Paul E. McKenney
2015-11-18 11:25 ` Will Deacon
2015-11-19 18:01 ` Will Deacon
2015-11-20 10:09 ` Peter Zijlstra
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