From: Mathieu Desnoyers <mathieu.desnoyers@efficios•com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: "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: Thu, 5 Oct 2017 16:02:06 +0000 (UTC) [thread overview]
Message-ID: <312162.31738.1507219326334.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20171005121250.prr5ff5kf3lxq6hx@hirez.programming.kicks-ass.net>
----- On Oct 5, 2017, at 8:12 AM, Peter Zijlstra peterz@infradead•org wrote:
> On Wed, Oct 04, 2017 at 02:37:53PM -0700, Paul E. McKenney wrote:
>> diff --git a/arch/powerpc/kernel/membarrier.c b/arch/powerpc/kernel/membarrier.c
>> new file mode 100644
>> index 000000000000..b0d79a5f5981
>> --- /dev/null
>> +++ b/arch/powerpc/kernel/membarrier.c
>> @@ -0,0 +1,45 @@
>
>> +void membarrier_arch_register_private_expedited(struct task_struct *p)
>> +{
>> + struct task_struct *t;
>> +
>> + if (get_nr_threads(p) == 1) {
>> + set_thread_flag(TIF_MEMBARRIER_PRIVATE_EXPEDITED);
>> + return;
>> + }
>> + /*
>> + * Coherence of TIF_MEMBARRIER_PRIVATE_EXPEDITED against thread
>> + * fork is protected by siglock.
>> + */
>> + spin_lock(&p->sighand->siglock);
>> + for_each_thread(p, t)
>> + set_ti_thread_flag(task_thread_info(t),
>> + TIF_MEMBARRIER_PRIVATE_EXPEDITED);
>
> I'm not sure this works correctly vs CLONE_VM without CLONE_THREAD.
The intent here is to hold the sighand siglock to provide mutual
exclusion against invocation of membarrier_fork(p, clone_flags)
by copy_process().
copy_process() grabs spin_lock(¤t->sighand->siglock) for both
CLONE_THREAD and not CLONE_THREAD flags.
What am I missing here ?
>
>> + spin_unlock(&p->sighand->siglock);
>> + /*
>> + * Ensure all future scheduler executions will observe the new
>> + * thread flag state for this process.
>> + */
>> + synchronize_sched();
>
> This relies on the flag being read inside rq->lock, right?
Yes. The flag is read by membarrier_arch_switch_mm(), invoked
within switch_mm_irqs_off(), called by context_switch() before
finish_task_switch() releases the rq lock.
Is the comment clear enough, or do you have suggestions for
improvements ?
Thanks,
Mathieu
>
> > +}
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2017-10-05 16:00 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 [this message]
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
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