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From: Valentin Schneider <valentin.schneider@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Quentin Perret <qperret@google.com>,
	linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Suren Baghdasaryan <surenb@google.com>, Tejun Heo <tj@kernel.org>,
	Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	kernel-team@android.com
Subject: Re: [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity
Date: Thu, 19 Nov 2020 11:27:55 +0000	[thread overview]
Message-ID: <jhja6vdwpqc.mognet@arm.com> (raw)
In-Reply-To: <20201119110549.GA3946@willie-the-truck>


On 19/11/20 11:05, Will Deacon wrote:
> On Thu, Nov 19, 2020 at 09:18:20AM +0000, Quentin Perret wrote:
>> > @@ -1937,20 +1931,69 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
>> >             * OK, since we're going to drop the lock immediately
>> >             * afterwards anyway.
>> >             */
>> > -		rq = move_queued_task(rq, &rf, p, dest_cpu);
>> > +		rq = move_queued_task(rq, rf, p, dest_cpu);
>> >    }
>> >  out:
>> > -	task_rq_unlock(rq, p, &rf);
>> > +	task_rq_unlock(rq, p, rf);
>>
>> And that's a little odd to have here no? Can we move it back on the
>> caller's side?
>
> I don't think so, unfortunately. __set_cpus_allowed_ptr_locked() can trigger
> migration, so it can drop the rq lock as part of that and end up relocking a
> new rq, which it also unlocks before returning. Doing the unlock in the
> caller is therfore even weirder, because you'd have to return the lock
> pointer or something horrible like that.
>
> I did add a comment about this right before the function and it's an
> internal function to the scheduler so I think it's ok.
>

An alternative here would be to add a new SCA_RESTRICT flag for
__set_cpus_allowed_ptr() (see migrate_disable() faff in
tip/sched/core). Not fond of either approaches, but the flag thing would
avoid this "quirk".

> Will

WARNING: multiple messages have this Message-ID (diff)
From: Valentin Schneider <valentin.schneider@arm.com>
To: Will Deacon <will@kernel.org>
Cc: linux-arch@vger.kernel.org, Juri Lelli <juri.lelli@redhat.com>,
	kernel-team@android.com,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Quentin Perret <qperret@google.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>,
	Ingo Molnar <mingo@redhat.com>, Li Zefan <lizefan@huawei.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Marc Zyngier <maz@kernel.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 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity
Date: Thu, 19 Nov 2020 11:27:55 +0000	[thread overview]
Message-ID: <jhja6vdwpqc.mognet@arm.com> (raw)
In-Reply-To: <20201119110549.GA3946@willie-the-truck>


On 19/11/20 11:05, Will Deacon wrote:
> On Thu, Nov 19, 2020 at 09:18:20AM +0000, Quentin Perret wrote:
>> > @@ -1937,20 +1931,69 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
>> >             * OK, since we're going to drop the lock immediately
>> >             * afterwards anyway.
>> >             */
>> > -		rq = move_queued_task(rq, &rf, p, dest_cpu);
>> > +		rq = move_queued_task(rq, rf, p, dest_cpu);
>> >    }
>> >  out:
>> > -	task_rq_unlock(rq, p, &rf);
>> > +	task_rq_unlock(rq, p, rf);
>>
>> And that's a little odd to have here no? Can we move it back on the
>> caller's side?
>
> I don't think so, unfortunately. __set_cpus_allowed_ptr_locked() can trigger
> migration, so it can drop the rq lock as part of that and end up relocking a
> new rq, which it also unlocks before returning. Doing the unlock in the
> caller is therfore even weirder, because you'd have to return the lock
> pointer or something horrible like that.
>
> I did add a comment about this right before the function and it's an
> internal function to the scheduler so I think it's ok.
>

An alternative here would be to add a new SCA_RESTRICT flag for
__set_cpus_allowed_ptr() (see migrate_disable() faff in
tip/sched/core). Not fond of either approaches, but the flag thing would
avoid this "quirk".

> Will

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  reply	other threads:[~2020-11-19 11:28 UTC|newest]

Thread overview: 104+ 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 ` 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   ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-13  9:37   ` Will Deacon
2020-11-19 11:27   ` Valentin Schneider
2020-11-19 11:27     ` Valentin Schneider
2020-11-19 13:12     ` Will Deacon
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   ` 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   ` 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   ` 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   ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon
2020-11-13  9:37   ` Will Deacon
2020-11-19  9:18   ` Quentin Perret
2020-11-19  9:18     ` Quentin Perret
2020-11-19 11:03     ` Quentin Perret
2020-11-19 11:03       ` Quentin Perret
2020-11-19 11:05     ` Will Deacon
2020-11-19 11:05       ` Will Deacon
2020-11-19 11:27       ` Valentin Schneider [this message]
2020-11-19 11:27         ` Valentin Schneider
2020-11-19 13:13         ` Will Deacon
2020-11-19 13:13           ` Will Deacon
2020-11-19 14:54           ` Valentin Schneider
2020-11-19 14:54             ` Valentin Schneider
2020-11-19 16:41             ` Will Deacon
2020-11-19 16:41               ` Will Deacon
2020-11-19 12:47   ` Valentin Schneider
2020-11-19 12:47     ` Valentin Schneider
2020-11-19 13:13     ` Will Deacon
2020-11-19 13:13       ` Will Deacon
2020-11-19 14:54       ` Valentin Schneider
2020-11-19 14:54         ` Valentin Schneider
2020-11-19 16:09       ` Peter Zijlstra
2020-11-19 16:09         ` Peter Zijlstra
2020-11-19 16:57         ` Valentin Schneider
2020-11-19 16:57           ` Valentin Schneider
2020-11-19 19:25           ` Will Deacon
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
2020-11-13  9:37   ` Will Deacon
2020-11-19  9:24   ` Quentin Perret
2020-11-19  9:24     ` Quentin Perret
2020-11-19 11:06     ` Will Deacon
2020-11-19 11:06       ` Will Deacon
2020-11-19 16:19       ` Peter Zijlstra
2020-11-19 16:19         ` Peter Zijlstra
2020-11-19 16:30         ` Will Deacon
2020-11-19 16:30           ` Will Deacon
2020-11-19 16:44           ` Peter Zijlstra
2020-11-19 16:44             ` Peter Zijlstra
2020-11-19 16:51             ` Will Deacon
2020-11-19 16:51               ` Will Deacon
2020-11-19 16:14   ` Peter Zijlstra
2020-11-19 16:14     ` Peter Zijlstra
2020-11-19 16:28     ` Will Deacon
2020-11-19 16:28       ` Will Deacon
2020-11-19 16:42       ` Peter Zijlstra
2020-11-19 16:42         ` Peter Zijlstra
2020-11-19 16:48         ` Will Deacon
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
2020-11-13  9:37   ` Will Deacon
2020-11-19  9:29   ` Quentin Perret
2020-11-19  9:29     ` Quentin Perret
2020-11-19 11:06     ` Will Deacon
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
2020-11-13  9:37   ` Will Deacon
2020-11-19  9:38   ` Quentin Perret
2020-11-19  9:38     ` Quentin Perret
2020-11-19 11:07     ` Will Deacon
2020-11-19 11:07       ` Will Deacon
2020-11-19 20:39       ` Will Deacon
2020-11-19 20:39         ` Will Deacon
2020-11-23 14:48         ` Quentin Perret
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
2020-11-13  9:37   ` Will Deacon
2020-11-19  9:47   ` Quentin Perret
2020-11-19  9:47     ` Quentin Perret
2020-11-19 11:07     ` Will Deacon
2020-11-19 11:07       ` Will Deacon
2020-11-19 14:30       ` Quentin Perret
2020-11-19 14:30         ` Quentin Perret
2020-11-19 16:44         ` Will Deacon
2020-11-19 16:44           ` Will Deacon
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   ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 13/14] arm64: Implement arch_cpu_allowed_mask() Will Deacon
2020-11-13  9:37   ` 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
2020-11-13  9:37   ` Will Deacon
2020-11-19 16:11 ` [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Peter Zijlstra
2020-11-19 16:11   ` Peter Zijlstra
2020-11-19 16:39   ` Will Deacon
2020-11-19 16:39     ` Will Deacon

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