From: Andrea Parri <parri.andrea@gmail•com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios•com>,
"Paul E. McKenney" <paulmck@linux•vnet.ibm.com>,
linux-kernel <linux-kernel@vger•kernel.org>,
Ingo Molnar <mingo@kernel•org>,
Lai Jiangshan <jiangshanlai@gmail•com>,
dipankar <dipankar@in•ibm.com>,
Andrew Morton <akpm@linux-foundation•org>,
Josh Triplett <josh@joshtriplett•org>,
Thomas Gleixner <tglx@linutronix•de>,
rostedt <rostedt@goodmis•org>,
David Howells <dhowells@redhat•com>,
Eric Dumazet <edumazet@google•com>, fweisbec <fweisbec@gmail•com>,
Oleg Nesterov <oleg@redhat•com>,
Boqun Feng <boqun.feng@gmail•com>, Andrew Hunter <ahh@google•com>,
maged michael <maged.michael@gmail•com>,
gromer <gromer@google•com>, Avi Kivity <avi@scylladb•com>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Paul Mackerras <paulus@samba•org>,
Michael Ellerman <mpe@ellerman•id.au>,
Dave Watson <davejwatson@fb•com>,
Alan Stern <stern@rowland•harvard.edu>,
Will Deacon <will.deacon@arm•com>,
Andy Lutomirski <luto@kernel•org>, Ingo Molnar <mingo@redhat•com>,
Alexander Viro <viro@zeniv•linux.org.uk>,
Nicholas Piggin <npiggin@gmail•com>,
linuxppc-dev <linuxppc-dev@lists•ozlabs.org>,
linux-arch <linux-arch@vger•kernel.org>
Subject: Re: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command
Date: Sat, 7 Oct 2017 17:10:04 +0200 [thread overview]
Message-ID: <20171007151004.GA3874@andrea> (raw)
In-Reply-To: <20171006083219.asdpl5w4pl6hedcd@hirez.programming.kicks-ass.net>
On Fri, Oct 06, 2017 at 10:32:19AM +0200, Peter Zijlstra wrote:
> > AFAIU the scheduler rq->lock is held while preemption is disabled.
> > synchronize_sched() is used here to ensure that all pre-existing
> > preempt-off critical sections have completed.
> >
> > So saying that we use synchronize_sched() to synchronize with rq->lock
> > would be stretching the truth a bit. It's actually only true because the
> > scheduler holding the rq->lock is surrounded by a preempt-off
> > critical section.
>
> No, rq->lock is sufficient, note that rq->lock is a raw_spinlock_t which
> implies !preempt. Yes, we also surround the rq->lock usage with a
> slightly larger preempt_disable() section but that's not in fact
> required for this.
That's what it is, according to the current sources: we seemed to agree that
a preempt-off critical section is what we rely on here and that the start of
this critical section is not marked by that raw_spin_lock.
Andrea
prev parent reply other threads:[~2017-10-07 15:10 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20171004213734.GA11463@linux.vnet.ibm.com>
2017-10-04 21:37 ` [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command Paul E. McKenney
2017-10-05 4:23 ` Nicholas Piggin
2017-10-05 12:22 ` Avi Kivity
2017-10-05 15:54 ` Mathieu Desnoyers
2017-10-05 15:53 ` Mathieu Desnoyers
2017-10-05 12:12 ` Peter Zijlstra
2017-10-05 12:24 ` Peter Zijlstra
2017-10-05 16:05 ` Mathieu Desnoyers
2017-10-05 16:02 ` Mathieu Desnoyers
2017-10-05 16:21 ` Peter Zijlstra
2017-10-05 21:44 ` Mathieu Desnoyers
2017-10-05 22:02 ` Andrea Parri
2017-10-05 22:04 ` Andrea Parri
2017-10-05 22:19 ` Mathieu Desnoyers
2017-10-05 22:46 ` Steven Rostedt
2017-10-06 8:32 ` Peter Zijlstra
2017-10-07 15:10 ` Andrea Parri [this message]
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