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From: Christoph Hellwig <hch@infradead.org>
To: Atish Patra <atish.patra@wdc.com>
Cc: "Christoph Hellwig" <hch@infradead.org>,
	"Patrick Stählin" <me@packi.ch>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Jason Cooper" <jason@lakedaemon.net>,
	"Alan Kao" <alankao@andestech.com>,
	"Dmitriy Cherkasov" <dmitriy@oss-tech.org>,
	"Anup Patel" <anup@brainfault.org>,
	"Daniel Lezcano" <daniel.lezcano@linaro.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Michael Clark" <michaeljclark@mac.com>,
	"Marc Zyngier" <marc.zyngier@arm.com>,
	"Palmer Dabbelt" <palmer@sifive.com>,
	"Andreas Schwab" <schwab@suse.de>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Zong Li" <zongbox@gmail.com>
Subject: Re: [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up
Date: Thu, 17 Jan 2019 23:20:38 -0800	[thread overview]
Message-ID: <20190118072038.GA5171@infradead.org> (raw)
In-Reply-To: <1995e941-a8cf-c12e-71ae-7b50cf6c0ca5@wdc.com>

On Thu, Jan 17, 2019 at 06:35:39PM -0800, Atish Patra wrote:
> On 1/15/19 5:51 AM, Christoph Hellwig wrote:
> > >   void *__cpu_up_stack_pointer[NR_CPUS];
> > >   void *__cpu_up_task_pointer[NR_CPUS];
> > > +static DECLARE_COMPLETION(cpu_running);
> > >   void __init smp_prepare_boot_cpu(void)
> > >   {
> > > @@ -81,6 +82,7 @@ void __init setup_smp(void)
> > >   int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> > >   {
> > > +	int ret = 0;
> > >   	int hartid = cpuid_to_hartid_map(cpu);
> > >   	tidle->thread_info.cpu = cpu;
> > > @@ -96,10 +98,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> > >   		  task_stack_page(tidle) + THREAD_SIZE);
> > >   	WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
> > > -	while (!cpu_online(cpu))
> > > -		cpu_relax();
> > > +	wait_for_completion_timeout(&cpu_running,
> > > +					    msecs_to_jiffies(1000));
> > 
> > Having a global completion here worries me.  I bet we have some higher
> > level serialization, but can we comment or even better lockdep assert on
> > that?
> > 
> 
> Yes. It is serialized from smp.c in smp_init(). It brings one cpu online
> at a time for preset_cpu mask.
> 
> Do we still need a lockdep assert ?

I guess the real lock is through cpu_hotplug_lock.  And yes, a comment
or even better lockdep assert would be good.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Atish Patra <atish.patra@wdc.com>
Cc: "Patrick Stählin" <me@packi.ch>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Jason Cooper" <jason@lakedaemon.net>,
	"Alan Kao" <alankao@andestech.com>,
	"Dmitriy Cherkasov" <dmitriy@oss-tech.org>,
	"Anup Patel" <anup@brainfault.org>,
	"Daniel Lezcano" <daniel.lezcano@linaro.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Michael Clark" <michaeljclark@mac.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Marc Zyngier" <marc.zyngier@arm.com>,
	"Palmer Dabbelt" <palmer@sifive.com>,
	"Andreas Schwab" <schwab@suse.de>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Zong Li" <zongbox@gmail.com>
Subject: Re: [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up
Date: Thu, 17 Jan 2019 23:20:38 -0800	[thread overview]
Message-ID: <20190118072038.GA5171@infradead.org> (raw)
In-Reply-To: <1995e941-a8cf-c12e-71ae-7b50cf6c0ca5@wdc.com>

On Thu, Jan 17, 2019 at 06:35:39PM -0800, Atish Patra wrote:
> On 1/15/19 5:51 AM, Christoph Hellwig wrote:
> > >   void *__cpu_up_stack_pointer[NR_CPUS];
> > >   void *__cpu_up_task_pointer[NR_CPUS];
> > > +static DECLARE_COMPLETION(cpu_running);
> > >   void __init smp_prepare_boot_cpu(void)
> > >   {
> > > @@ -81,6 +82,7 @@ void __init setup_smp(void)
> > >   int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> > >   {
> > > +	int ret = 0;
> > >   	int hartid = cpuid_to_hartid_map(cpu);
> > >   	tidle->thread_info.cpu = cpu;
> > > @@ -96,10 +98,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> > >   		  task_stack_page(tidle) + THREAD_SIZE);
> > >   	WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
> > > -	while (!cpu_online(cpu))
> > > -		cpu_relax();
> > > +	wait_for_completion_timeout(&cpu_running,
> > > +					    msecs_to_jiffies(1000));
> > 
> > Having a global completion here worries me.  I bet we have some higher
> > level serialization, but can we comment or even better lockdep assert on
> > that?
> > 
> 
> Yes. It is serialized from smp.c in smp_init(). It brings one cpu online
> at a time for preset_cpu mask.
> 
> Do we still need a lockdep assert ?

I guess the real lock is through cpu_hotplug_lock.  And yes, a comment
or even better lockdep assert would be good.

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  reply	other threads:[~2019-01-18  7:20 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-08  9:38 [PATCH v2 0/8] Various SMP related fixes Atish Patra
2019-01-08  9:38 ` Atish Patra
2019-01-08  9:38 ` [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-15 13:51   ` Christoph Hellwig
2019-01-15 13:51     ` Christoph Hellwig
2019-01-18  2:35     ` Atish Patra
2019-01-18  2:35       ` Atish Patra
2019-01-18  7:20       ` Christoph Hellwig [this message]
2019-01-18  7:20         ` Christoph Hellwig
2019-01-08  9:38 ` [PATCH v2 2/8] RISC-V: Move cpuid to hartid mapping to SMP Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-15 13:52   ` Christoph Hellwig
2019-01-15 13:52     ` Christoph Hellwig
2019-01-18  2:08     ` Atish Patra
2019-01-18  2:08       ` Atish Patra
2019-01-08  9:38 ` [PATCH v2 3/8] RISC-V: Remove NR_CPUs check during hartid search from DT Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-08 11:48   ` Anup Patel
2019-01-08 11:48     ` Anup Patel
2019-01-15 13:52   ` Christoph Hellwig
2019-01-15 13:52     ` Christoph Hellwig
2019-01-08  9:38 ` [PATCH v2 4/8] RISC-V: Allow hartid-to-cpuid function to fail Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-08 11:49   ` Anup Patel
2019-01-08 11:49     ` Anup Patel
2019-01-15 13:53   ` Christoph Hellwig
2019-01-15 13:53     ` Christoph Hellwig
2019-01-08  9:38 ` [PATCH v2 5/8] RISC-V: Compare cpuid with NR_CPUS before mapping Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-08 11:49   ` Anup Patel
2019-01-08 11:49     ` Anup Patel
2019-01-15 13:53   ` Christoph Hellwig
2019-01-15 13:53     ` Christoph Hellwig
2019-01-08  9:38 ` [PATCH v2 6/8] RISC-V: Add required checks during clock source init Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-08 11:56   ` Anup Patel
2019-01-08 11:56     ` Anup Patel
2019-01-18  2:10     ` Atish Patra
2019-01-18  2:10       ` Atish Patra
2019-01-15 13:54   ` Christoph Hellwig
2019-01-15 13:54     ` Christoph Hellwig
2019-01-08  9:38 ` [PATCH v2 7/8] RISC-V: Check and continue in case of an invalid cpuid Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-08 11:59   ` Anup Patel
2019-01-08 11:59     ` Anup Patel
2019-01-18  2:10     ` Atish Patra
2019-01-18  2:10       ` Atish Patra
2019-01-15 13:55   ` Christoph Hellwig
2019-01-15 13:55     ` Christoph Hellwig
2019-01-08  9:38 ` [PATCH v2 8/8] RISC-V: Assign hwcap only according to current cpu Atish Patra
2019-01-08  9:38   ` Atish Patra
2019-01-08 10:33   ` Atish Patra
2019-01-08 10:33     ` Atish Patra
2019-01-08 12:01   ` Anup Patel
2019-01-08 12:01     ` Anup Patel
2019-01-15 13:56   ` Christoph Hellwig
2019-01-15 13:56     ` Christoph Hellwig
2019-01-18  2:13     ` Atish Patra
2019-01-18  2:13       ` Atish Patra

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