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From: Will Deacon <will@kernel.org>
To: Quentin Perret <qperret@google.com>
Cc: linux-arch@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	kernel-team@android.com,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	linux-kernel@vger.kernel.org, Qais Yousef <qais.yousef@arm.com>,
	Li Zefan <lizefan@huawei.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tejun Heo <tj@kernel.org>, Suren Baghdasaryan <surenb@google.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 11/14] sched: Reject CPU affinity changes based on arch_cpu_allowed_mask()
Date: Thu, 19 Nov 2020 16:44:13 +0000	[thread overview]
Message-ID: <20201119164412.GE4582@willie-the-truck> (raw)
In-Reply-To: <20201119143012.GA2458028@google.com>

On Thu, Nov 19, 2020 at 02:30:12PM +0000, Quentin Perret wrote:
> On Thursday 19 Nov 2020 at 11:07:24 (+0000), Will Deacon wrote:
> > Yeah, the cpuset code ignores the return value of set_cpus_allowed_ptr() in
> > update_tasks_cpumask() so the failure won't be propagated, but then again I
> > think that might be the right thing to do. Nothing prevents 32-bit and
> > 64-bit tasks from co-existing in the same cpuseti afaict, so forcing the
> > 64-bit tasks onto the 32-bit-capable cores feels much worse than the
> > approach taken here imo.
> 
> Ack. And thinking about it more, failing the cgroup operation wouldn't
> guarantee that the task's affinity and the cpuset are aligned anyway. We
> could still exec into a 32 bit task from within a 64 bit-only cpuset.
> 
> > The interesting case is what happens if the cpuset for a 32-bit task is
> > changed to contain only the 64-bit-only cores. I think that's a userspace
> > bug
> 
> Maybe, but I think Android will do exactly that in some cases :/
> 
> > but the fallback rq selection should avert disaster.
> 
> I thought _this_ patch was 'fixing' this case by making the cpuset
> operation pretty much a nop on the task affinity? The fallback rq stuff
> is all about hotplug no?

Yeah, sorry, I wasn't clear. This patch postpones disaster until hotplug
off time, when cpuset_cpus_allowed_fallback() will fail and
select_fallback_rq() will have to step in.

Will

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  reply	other threads:[~2020-11-19 16:45 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13  9:37 [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Will Deacon
2020-11-13  9:37 ` [PATCH v3 01/14] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2020-11-13  9:37 ` [PATCH v3 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-19 11:27   ` Valentin Schneider
2020-11-19 13:12     ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2020-11-13  9:37 ` [PATCH v3 04/14] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2020-11-13  9:37 ` [PATCH v3 05/14] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2020-11-13  9:37 ` [PATCH v3 06/14] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2020-11-13  9:37 ` [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon
2020-11-19  9:18   ` Quentin Perret
2020-11-19 11:03     ` Quentin Perret
2020-11-19 11:05     ` Will Deacon
2020-11-19 11:27       ` Valentin Schneider
2020-11-19 13:13         ` Will Deacon
2020-11-19 14:54           ` Valentin Schneider
2020-11-19 16:41             ` Will Deacon
2020-11-19 12:47   ` Valentin Schneider
2020-11-19 13:13     ` Will Deacon
2020-11-19 14:54       ` Valentin Schneider
2020-11-19 16:09       ` Peter Zijlstra
2020-11-19 16:57         ` Valentin Schneider
2020-11-19 19:25           ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2020-11-19  9:24   ` Quentin Perret
2020-11-19 11:06     ` Will Deacon
2020-11-19 16:19       ` Peter Zijlstra
2020-11-19 16:30         ` Will Deacon
2020-11-19 16:44           ` Peter Zijlstra
2020-11-19 16:51             ` Will Deacon
2020-11-19 16:14   ` Peter Zijlstra
2020-11-19 16:28     ` Will Deacon
2020-11-19 16:42       ` Peter Zijlstra
2020-11-19 16:48         ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2020-11-19  9:29   ` Quentin Perret
2020-11-19 11:06     ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 10/14] sched: Introduce arch_cpu_allowed_mask() to limit fallback rq selection Will Deacon
2020-11-19  9:38   ` Quentin Perret
2020-11-19 11:07     ` Will Deacon
2020-11-19 20:39       ` Will Deacon
2020-11-23 14:48         ` Quentin Perret
2020-11-13  9:37 ` [PATCH v3 11/14] sched: Reject CPU affinity changes based on arch_cpu_allowed_mask() Will Deacon
2020-11-19  9:47   ` Quentin Perret
2020-11-19 11:07     ` Will Deacon
2020-11-19 14:30       ` Quentin Perret
2020-11-19 16:44         ` Will Deacon [this message]
2020-11-13  9:37 ` [PATCH v3 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2020-11-13  9:37 ` [PATCH v3 13/14] arm64: Implement arch_cpu_allowed_mask() Will Deacon
2020-11-13  9:37 ` [PATCH v3 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2020-11-19 16:11 ` [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Peter Zijlstra
2020-11-19 16:39   ` Will Deacon

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