From: David Woodhouse <dwmw2@infradead.org>
To: paulmck@kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
"Schander, Johanna 'Mimoja' Amelie" <mimoja@amazon.com>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
hewenliang4@huawei.com, hushiyuan@huawei.com,
luolongjun@huawei.com, hejingxian <hejingxian@huawei.com>
Subject: Re: [PATCH] use x86 cpu park to speedup smp_init in kexec situation
Date: Wed, 08 Dec 2021 16:57:07 +0000 [thread overview]
Message-ID: <f67ce85c73941bd5d35e8af84765c70f56ddcdf7.camel@infradead.org> (raw)
In-Reply-To: <0824902894565e850b79e494c38a7856f8358b99.camel@infradead.org>
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On Wed, 2021-12-08 at 15:10 +0000, David Woodhouse wrote:
> @@ -4266,13 +4266,13 @@ void rcu_cpu_starting(unsigned int cpu)
> rcu_disable_urgency_upon_qs(rdp);
> /* Report QS -after- changing ->qsmaskinitnext! */
> rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
> + /* Er, why didn't we drop the lock here? */
> - } else {
> - raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> }
>
Oh, I see... how about this straw man then...
From 083c8fb2656e9fc60a17c9bfd538fcee4c5ebacc Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Tue, 16 Feb 2021 15:04:34 +0000
Subject: [PATCH 1/4] rcu: Expand locking around rcu_cpu_starting() to cover
rnp->ofl_seq bump
To allow architectures to bring APs online in parallel, we need only one
of them to be going through rcu_cpu_starting() at a time. Expand the
coverage of the existing per-node lock to cover the manipulation of
rnp->ofl_seq too.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
kernel/rcu/tree.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ef8d36f580fc..544198c674f2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4246,11 +4246,11 @@ void rcu_cpu_starting(unsigned int cpu)
rnp = rdp->mynode;
mask = rdp->grpmask;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
WARN_ON_ONCE(!(rnp->ofl_seq & 0x1));
rcu_dynticks_eqs_online();
smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
newcpu = !(rnp->expmaskinitnext & mask);
rnp->expmaskinitnext |= mask;
@@ -4261,6 +4261,11 @@ void rcu_cpu_starting(unsigned int cpu)
rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
+ smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
+ WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
+ WARN_ON_ONCE(rnp->ofl_seq & 0x1);
+ smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
+
/* An incoming CPU should never be blocking a grace period. */
if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
rcu_disable_urgency_upon_qs(rdp);
@@ -4269,10 +4274,6 @@ void rcu_cpu_starting(unsigned int cpu)
} else {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
- smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
- WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
- WARN_ON_ONCE(rnp->ofl_seq & 0x1);
- smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
}
/*
--
2.31.1
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next prev parent reply other threads:[~2021-12-08 16:57 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <87ft22dxop.fsf@nanos.tec.linutronix.de>
[not found] ` <27357c74bdc3b52bdf59e6f48cd8690495116d64.camel@infradead.org>
[not found] ` <877dnedt7l.fsf@nanos.tec.linutronix.de>
[not found] ` <87zh09tcqz.fsf@nanos.tec.linutronix.de>
2021-02-16 13:53 ` [PATCH] use x86 cpu park to speedup smp_init in kexec situation David Woodhouse
2021-02-16 15:10 ` David Woodhouse
2021-02-16 21:18 ` David Woodhouse
2021-12-08 14:14 ` David Woodhouse
2021-12-08 14:50 ` Paul E. McKenney
2021-12-08 15:10 ` David Woodhouse
2021-12-08 16:57 ` David Woodhouse [this message]
2021-12-08 17:35 ` Paul E. McKenney
2021-12-08 18:32 ` David Woodhouse
2021-12-08 19:03 ` Paul E. McKenney
2021-12-08 20:35 ` David Woodhouse
2021-12-08 21:09 ` Paul E. McKenney
2020-12-15 14:46 shenkai (D)
2020-12-15 16:31 ` Andy Lutomirski
2020-12-15 21:20 ` Thomas Gleixner
2020-12-16 8:45 ` shenkai (D)
2020-12-16 10:12 ` Thomas Gleixner
2020-12-16 14:18 ` shenkai (D)
2020-12-16 15:31 ` Thomas Gleixner
2020-12-17 14:53 ` shenkai (D)
2021-01-07 15:18 ` David Woodhouse
2021-01-19 12:12 ` David Woodhouse
2021-01-21 14:55 ` Thomas Gleixner
2021-01-21 15:42 ` David Woodhouse
2021-01-21 17:34 ` David Woodhouse
2021-02-01 10:36 ` David Woodhouse
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