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From: Will Deacon <will@kernel.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: 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>,
	Suren Baghdasaryan <surenb@google.com>,
	Quentin Perret <qperret@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>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	kernel-team@android.com
Subject: Re: [PATCH v6 12/21] sched: Allow task CPU affinity to be restricted on asymmetric systems
Date: Mon, 24 May 2021 22:43:49 +0100	[thread overview]
Message-ID: <20210524214348.GH15545@willie-the-truck> (raw)
In-Reply-To: <20210521171132.ev56j4isuxtf2zqa@e107158-lin.cambridge.arm.com>

On Fri, May 21, 2021 at 06:11:32PM +0100, Qais Yousef wrote:
> On 05/18/21 10:47, Will Deacon wrote:
> > +static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
> > +					 const struct cpumask *new_mask,
> > +					 u32 flags,
> > +					 struct rq *rq,
> > +					 struct rq_flags *rf)
> > +	__releases(rq->lock)
> > +	__releases(p->pi_lock)
> >  {
> >  	const struct cpumask *cpu_valid_mask = cpu_active_mask;
> >  	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
> >  	unsigned int dest_cpu;
> > -	struct rq_flags rf;
> > -	struct rq *rq;
> >  	int ret = 0;
> >  
> > -	rq = task_rq_lock(p, &rf);
> >  	update_rq_clock(rq);
> >  
> >  	if (p->flags & PF_KTHREAD || is_migration_disabled(p)) {
> > @@ -2430,20 +2425,158 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
> >  
> >  	__do_set_cpus_allowed(p, new_mask, flags);
> >  
> > -	return affine_move_task(rq, p, &rf, dest_cpu, flags);
> > +	if (flags & SCA_USER)
> > +		release_user_cpus_ptr(p);
> 
> Why do we need to release the pointer here?
> 
> Doesn't this mean if a 32bit task requests to change its affinity, then we'll
> lose this info and a subsequent execve() to a 64bit application means we won't
> be able to restore the original mask?
> 
> ie:
> 
> 	p0-64bit
> 	  execve(32bit_app)
> 	    // p1-32bit created
> 	    p1-32bit.change_affinity()
> 	      relase_user_cpus_ptr()
> 	    execve(64bit_app)           // lost info about p0 affinity?
> 
> Hmm I think this helped me to get the answer. p1 changed its affinity, then
> there's nothing to be inherited by a new execve(), so yes we no longer need
> this info.

Yup, you got it.

> > +static int restrict_cpus_allowed_ptr(struct task_struct *p,
> > +				     struct cpumask *new_mask,
> > +				     const struct cpumask *subset_mask)
> > +{
> > +	struct rq_flags rf;
> > +	struct rq *rq;
> > +	int err;
> > +	struct cpumask *user_mask = NULL;
> > +
> > +	if (!p->user_cpus_ptr)
> > +		user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> > +
> > +	rq = task_rq_lock(p, &rf);
> > +
> > +	/*
> > +	 * We're about to butcher the task affinity, so keep track of what
> > +	 * the user asked for in case we're able to restore it later on.
> > +	 */
> > +	if (user_mask) {
> > +		cpumask_copy(user_mask, p->cpus_ptr);
> > +		p->user_cpus_ptr = user_mask;
> > +	}
> > +
> > +	/*
> > +	 * Forcefully restricting the affinity of a deadline task is
> > +	 * likely to cause problems, so fail and noisily override the
> > +	 * mask entirely.
> > +	 */
> > +	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
> > +		err = -EPERM;
> > +		goto err_unlock;
> 
> free(user_mark) first?
> 
> > +	}
> > +
> > +	if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
> > +		err = -EINVAL;
> > +		goto err_unlock;
> 
> ditto

We free the mask when the task exits so we don't actually need to clean up
here. I left it like this on the assumption that failing here means that
it's very likely that either the task will exit or retry very soon.

However I agree that it would be clearer to free the thing anyway, so I'll
rejig the code to do that.

Will

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  reply	other threads:[~2021-05-25  2:19 UTC|newest]

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-18  9:47 [PATCH v6 00/21] Add support for 32-bit tasks on asymmetric AArch32 systems Will Deacon
2021-05-18  9:47 ` [PATCH v6 01/21] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2021-05-21 10:47   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 02/21] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2021-05-21 10:25   ` Catalin Marinas
2021-05-24 12:05     ` Will Deacon
2021-05-24 13:49       ` Catalin Marinas
2021-05-21 10:41   ` Catalin Marinas
2021-05-24 12:09     ` Will Deacon
2021-05-24 13:46       ` Catalin Marinas
2021-05-21 15:22   ` Qais Yousef
2021-05-24 20:21     ` Will Deacon
2021-05-18  9:47 ` [PATCH v6 03/21] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2021-05-21 10:47   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 04/21] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2021-05-21 10:55   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 05/21] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2021-05-21 11:00   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 06/21] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Will Deacon
2021-05-21 16:03   ` Peter Zijlstra
2021-05-24 12:17     ` Will Deacon
2021-05-18  9:47 ` [PATCH v6 07/21] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2021-05-21 17:39   ` Qais Yousef
2021-05-24 20:21     ` Will Deacon
2021-05-18  9:47 ` [PATCH v6 08/21] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus() Will Deacon
2021-05-21 16:25   ` Qais Yousef
2021-05-24 21:09     ` Will Deacon
2021-05-18  9:47 ` [PATCH v6 09/21] sched: Reject CPU affinity changes based on task_cpu_possible_mask() Will Deacon
2021-05-18  9:47 ` [PATCH v6 10/21] sched: Introduce task_struct::user_cpus_ptr to track requested affinity Will Deacon
2021-05-18  9:47 ` [PATCH v6 11/21] sched: Split the guts of sched_setaffinity() into a helper function Will Deacon
2021-05-21 16:41   ` Qais Yousef
2021-05-24 21:16     ` Will Deacon
2021-05-18  9:47 ` [PATCH v6 12/21] sched: Allow task CPU affinity to be restricted on asymmetric systems Will Deacon
2021-05-21 17:11   ` Qais Yousef
2021-05-24 21:43     ` Will Deacon [this message]
2021-05-18  9:47 ` [PATCH v6 13/21] sched: Admit forcefully-affined tasks into SCHED_DEADLINE Will Deacon
2021-05-18 10:20   ` Quentin Perret
2021-05-18 10:28     ` Will Deacon
2021-05-18 10:48       ` Quentin Perret
2021-05-18 10:59         ` Will Deacon
2021-05-18 13:19           ` Quentin Perret
2021-05-20  9:13             ` Juri Lelli
2021-05-20 10:16               ` Will Deacon
2021-05-20 10:33                 ` Quentin Perret
2021-05-20 12:38                   ` Juri Lelli
2021-05-20 12:38                   ` Daniel Bristot de Oliveira
2021-05-20 15:06                     ` Dietmar Eggemann
2021-05-20 16:00                       ` Daniel Bristot de Oliveira
2021-05-20 17:55                         ` Dietmar Eggemann
2021-05-20 18:03                           ` Will Deacon
2021-05-21 11:26                             ` Dietmar Eggemann
2021-05-20 18:01                     ` Will Deacon
2021-05-21  5:25                       ` Juri Lelli
2021-05-21  8:15                         ` Quentin Perret
2021-05-21  8:39                           ` Juri Lelli
2021-05-21 10:37                             ` Will Deacon
2021-05-21 11:23                               ` Dietmar Eggemann
2021-05-21 13:02                                 ` Quentin Perret
2021-05-21 14:04                                   ` Juri Lelli
2021-05-21 17:47                                     ` Dietmar Eggemann
2021-05-21 13:00                               ` Daniel Bristot de Oliveira
2021-05-21 13:12                                 ` Quentin Perret
2021-05-24 20:47                                 ` Will Deacon
2021-05-18  9:47 ` [PATCH v6 14/21] freezer: Add frozen_or_skipped() helper function Will Deacon
2021-05-18  9:47 ` [PATCH v6 15/21] sched: Defer wakeup in ttwu() for unschedulable frozen tasks Will Deacon
2021-05-18  9:47 ` [PATCH v6 16/21] arm64: Implement task_cpu_possible_mask() Will Deacon
2021-05-24 14:57   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 17/21] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2021-05-24 15:02   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 18/21] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2021-05-24 15:46   ` Catalin Marinas
2021-05-24 20:32     ` Will Deacon
2021-05-25  9:43       ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 19/21] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2021-05-24 15:47   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 20/21] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2021-05-24 15:47   ` Catalin Marinas
2021-05-18  9:47 ` [PATCH v6 21/21] Documentation: arm64: describe asymmetric 32-bit support Will Deacon
2021-05-21 17:37   ` Qais Yousef
2021-05-24 21:46     ` Will Deacon
2021-05-24 16:22   ` Catalin Marinas
2021-05-21 17:45 ` [PATCH v6 00/21] Add support for 32-bit tasks on asymmetric AArch32 systems Qais Yousef
2021-05-24 22:08   ` Will Deacon

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