From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Balbir Singh <bsingharora@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Nicholas Piggin <nicholas.piggin@gmail.com>
Subject: Re: [RFC][PATCH] Fix a race between rwsem and the scheduler
Date: Tue, 30 Aug 2016 15:04:27 +0200 [thread overview]
Message-ID: <20160830130426.GA17795@redhat.com> (raw)
In-Reply-To: <20160830121937.GQ10138@twins.programming.kicks-ass.net>
On 08/30, Peter Zijlstra wrote:
>
> /*
> * Ensure we load p->on_rq _after_ p->state, otherwise it would
> * be possible to, falsely, observe p->on_rq == 0 and get stuck
> * in smp_cond_load_acquire() below.
> *
> * sched_ttwu_pending() try_to_wake_up()
> * [S] p->on_rq = 1; [L] P->state
> * UNLOCK rq->lock
> *
> * schedule() RMB
> * LOCK rq->lock
> * UNLOCK rq->lock
> *
> * [task p]
> * [S] p->state = UNINTERRUPTIBLE [L] p->on_rq
> *
> * Pairs with the UNLOCK+LOCK on rq->lock from the
> * last wakeup of our task and the schedule that got our task
> * current.
> */
Confused... how this connects to UNLOCK+LOCK on rq->lock? A LOAD can
leak into the critical section.
But context switch should imply mb() we can rely on?
Oleg.
next prev parent reply other threads:[~2016-08-30 13:05 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-30 8:49 [RFC][PATCH] Fix a race between rwsem and the scheduler Balbir Singh
2016-08-30 9:13 ` Nicholas Piggin
2016-08-30 12:19 ` Peter Zijlstra
2016-08-30 13:04 ` Oleg Nesterov [this message]
2016-08-30 14:13 ` Peter Zijlstra
2016-08-30 16:57 ` Oleg Nesterov
2016-08-30 18:34 ` Peter Zijlstra
2016-08-30 21:28 ` Benjamin Herrenschmidt
2016-08-31 7:18 ` Peter Zijlstra
2016-08-31 10:56 ` Benjamin Herrenschmidt
2016-08-31 13:31 ` Peter Zijlstra
2016-08-31 21:47 ` Benjamin Herrenschmidt
2016-09-01 6:49 ` Balbir Singh
2016-09-01 6:57 ` Peter Zijlstra
2016-09-01 14:17 ` Boqun Feng
2016-09-01 15:33 ` Peter Zijlstra
2016-08-30 21:25 ` Benjamin Herrenschmidt
2016-08-31 7:20 ` Peter Zijlstra
2016-08-31 10:55 ` Benjamin Herrenschmidt
2016-08-31 3:41 ` Balbir Singh
2016-08-31 7:28 ` Peter Zijlstra
2016-08-31 10:17 ` Balbir Singh
2016-08-31 10:57 ` Benjamin Herrenschmidt
2016-09-01 1:48 ` Alexey Kardashevskiy
2016-09-01 12:16 ` Alexey Kardashevskiy
2016-08-30 12:58 ` Oleg Nesterov
2016-08-31 3:25 ` Balbir Singh
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