From: Will Deacon <will@kernel.org>
To: Quentin Perret <qperret@google.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>,
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 11/14] sched: Reject CPU affinity changes based on arch_cpu_allowed_mask()
Date: Thu, 19 Nov 2020 11:07:24 +0000 [thread overview]
Message-ID: <20201119110723.GE3946@willie-the-truck> (raw)
In-Reply-To: <20201119094744.GE2416649@google.com>
On Thu, Nov 19, 2020 at 09:47:44AM +0000, Quentin Perret wrote:
> On Friday 13 Nov 2020 at 09:37:16 (+0000), Will Deacon wrote:
> > Reject explicit requests to change the affinity mask of a task via
> > set_cpus_allowed_ptr() if the requested mask is not a subset of the
> > mask returned by arch_cpu_allowed_mask(). This ensures that the
> > 'cpus_mask' for a given task cannot contain CPUs which are incapable of
> > executing it, except in cases where the affinity is forced.
> >
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> > kernel/sched/core.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 8df38ebfe769..13bdb2ae4d3f 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1877,6 +1877,7 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
> > struct rq_flags *rf)
> > {
> > const struct cpumask *cpu_valid_mask = cpu_active_mask;
> > + const struct cpumask *cpu_allowed_mask = arch_cpu_allowed_mask(p);
> > unsigned int dest_cpu;
> > int ret = 0;
> >
> > @@ -1887,6 +1888,9 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
> > * Kernel threads are allowed on online && !active CPUs
> > */
> > cpu_valid_mask = cpu_online_mask;
> > + } else if (!cpumask_subset(new_mask, cpu_allowed_mask)) {
> > + ret = -EINVAL;
> > + goto out;
>
> So, IIUC, this should make the sched_setaffinity() syscall fail and
> return -EINVAL to userspace if it tries to put 64bits CPUs in the
> affinity mask of a 32 bits task, which I think makes sense.
>
> But what about affinity change via cpusets? e.g., if a 32 bit task is
> migrated to a cpuset with 64 bit CPUs, then the migration will be
> 'successful' and the task will appear to be in the destination cgroup,
> but the actual affinity of the task will be something completely
> different?
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. Nothing says we _have_ to schedule on all of the
cores in the mask.
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, but the fallback rq selection should avert disaster.
Will
next prev parent reply other threads:[~2020-11-19 11:07 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 [this message]
2020-11-19 14:30 ` Quentin Perret
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 ` [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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