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From: Alex Belits <abelits@marvell.com>
To: "frederic@kernel.org" <frederic@kernel.org>
Cc: "mingo@kernel.org" <mingo@kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"Prasun Kapoor" <pkapoor@marvell.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"will@kernel.org" <will@kernel.org>
Subject: Re: [EXT] Re: [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus
Date: Sun, 8 Mar 2020 06:48:43 +0000
Message-ID: <7e0ce8988f4811e7453859e22654d2618557d9ab.camel@marvell.com> (raw)
In-Reply-To: <20200306153446.GC8590@lenoir>

On Fri, 2020-03-06 at 16:34 +0100, Frederic Weisbecker wrote:
> On Wed, Mar 04, 2020 at 04:15:24PM +0000, Alex Belits wrote:
> > From: Yuri Norov <ynorov@marvell.com>
> > 
> > Make sure that kick_all_cpus_sync() does not call CPUs that are
> > running
> > isolated tasks.
> > 
> > Signed-off-by: Alex Belits <abelits@marvell.com>
> > ---
> >  kernel/smp.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/smp.c b/kernel/smp.c
> > index 3a8bcbdd4ce6..d9b4b2fedfed 100644
> > --- a/kernel/smp.c
> > +++ b/kernel/smp.c
> > @@ -731,9 +731,21 @@ static void do_nothing(void *unused)
> >   */
> >  void kick_all_cpus_sync(void)
> >  {
> > +	struct cpumask mask;
> > +
> >  	/* Make sure the change is visible before we kick the cpus */
> >  	smp_mb();
> > -	smp_call_function(do_nothing, NULL, 1);
> > +
> > +	preempt_disable();
> > +#ifdef CONFIG_TASK_ISOLATION
> > +	cpumask_clear(&mask);
> > +	task_isolation_cpumask(&mask);
> > +	cpumask_complement(&mask, &mask);
> > +#else
> > +	cpumask_setall(&mask);
> > +#endif
> > +	smp_call_function_many(&mask, do_nothing, NULL, 1);
> > +	preempt_enable();
> >  }
> 
> That looks very dangerous, the callers of kick_all_cpus_sync() want
> to
> sync all CPUs for a reason. You will rather need to fix the callers.

All callers of this use this function to synchronize IPIs and icache,
and they have no idea if there is anything special about the state of
CPUs. If a task is isolated, this call would not be necessary because
the task is in userspace, and it would have to enter kernel for any of
that to become relevant but then it will have to switch from userspace
to kernel. At worst it is returning to userspace after entering
isolation or back in kernel running cleanup after isolation is broken
but before tsk_thread_flags_cache is updated. There will be nothing to
run on the same CPU because we have just left isolation, so task will
either exit or go back to userspace.

Is there any reason for a race at that point?

> Thanks.
> 
> >  EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
> >  
> > -- 
> > 2.20.1
> > 

-- 
Alex

  reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-04 16:01 [PATCH 00/12] "Task_isolation" mode Alex Belits
2020-03-04 16:03 ` [PATCH 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-03-04 16:04 ` [PATCH 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-03-04 16:07 ` [PATCH 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
2020-03-05 18:33   ` Frederic Weisbecker
2020-03-08  5:32     ` [EXT] " Alex Belits
2020-04-28 14:12     ` Marcelo Tosatti
2020-03-06 15:26   ` Frederic Weisbecker
2020-03-08  6:06     ` [EXT] " Alex Belits
2020-03-06 16:00   ` Frederic Weisbecker
2020-03-08  7:16     ` [EXT] " Alex Belits
2020-03-04 16:08 ` [PATCH 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-03-04 16:09 ` [PATCH 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-03-04 16:10 ` [PATCH 06/12] task_isolation: arch/arm64: " Alex Belits
2020-03-04 16:31   ` Mark Rutland
2020-03-08  4:48     ` [EXT] " Alex Belits
2020-03-04 16:11 ` [PATCH 07/12] task_isolation: arch/arm: " Alex Belits
2020-03-04 16:12 ` [PATCH 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-06 16:03   ` Frederic Weisbecker
2020-03-08  7:28     ` [EXT] " Alex Belits
2020-03-09  2:38       ` Frederic Weisbecker
2020-03-04 16:13 ` [PATCH 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-03-04 16:14 ` [PATCH 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-03-04 16:15 ` [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-06 15:34   ` Frederic Weisbecker
2020-03-08  6:48     ` Alex Belits [this message]
2020-03-09  2:28       ` [EXT] " Frederic Weisbecker
2020-03-04 16:16 ` [PATCH 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
2020-03-08  3:42 ` [PATCH v2 00/12] "Task_isolation" mode Alex Belits
2020-03-08  3:44   ` [PATCH v2 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-03-08  3:46   ` [PATCH v2 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-03-08  3:47   ` [PATCH v2 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
     [not found]     ` <20200307214254.7a8f6c22@hermes.lan>
2020-03-08  7:33       ` [EXT] " Alex Belits
2020-03-27  8:42     ` Marta Rybczynska
2020-04-06  4:31     ` Kevyn-Alexandre Paré
2020-04-06  4:43     ` Kevyn-Alexandre Paré
2020-03-08  3:48   ` [PATCH v2 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-03-08  3:49   ` [PATCH v2 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-03-08  3:50   ` [PATCH v2 06/12] task_isolation: arch/arm64: " Alex Belits
2020-03-09 16:59     ` Mark Rutland
2020-03-08  3:52   ` [PATCH v2 07/12] task_isolation: arch/arm: " Alex Belits
2020-03-08  3:53   ` [PATCH v2 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-08  3:54   ` [PATCH v2 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-03-08  3:55   ` [PATCH v2 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-04-06  4:27     ` Kevyn-Alexandre Paré
2020-03-08  3:56   ` [PATCH v2 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-08  3:57   ` [PATCH v2 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
2020-04-09 15:09   ` [PATCH v3 00/13] "Task_isolation" mode Alex Belits
2020-04-09 15:15     ` [PATCH 01/13] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-04-09 15:16     ` [PATCH 02/13] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-04-09 15:17     ` [PATCH v3 03/13] task_isolation: add instruction synchronization memory barrier Alex Belits
2020-04-15 12:44       ` Mark Rutland
2020-04-19  5:02         ` [EXT] " Alex Belits
2020-04-20 12:23           ` Will Deacon
2020-04-20 12:36             ` Mark Rutland
2020-04-20 13:55               ` Will Deacon
2020-04-21  7:41                 ` Will Deacon
2020-04-20 12:45           ` Mark Rutland
2020-04-09 15:20     ` [PATCH v3 04/13] task_isolation: userspace hard isolation from kernel Alex Belits
2020-04-09 18:00       ` Andy Lutomirski
2020-04-19  5:07         ` Alex Belits
2020-04-09 15:21     ` [PATCH 05/13] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-04-09 15:22     ` [PATCH 06/13] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-04-09 15:23     ` [PATCH v3 07/13] task_isolation: arch/arm64: " Alex Belits
2020-04-22 12:08       ` Catalin Marinas
2020-04-09 15:24     ` [PATCH v3 08/13] task_isolation: arch/arm: " Alex Belits
2020-04-09 15:25     ` [PATCH v3 09/13] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-04-09 15:26     ` [PATCH v3 10/13] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-04-09 15:27     ` [PATCH v3 11/13] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-04-09 15:27     ` [PATCH v3 12/13] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-04-09 15:28     ` [PATCH v3 13/13] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits

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