linux-kernel - [PATCH v6 09/21] sched: Reject CPU affinity changes based on task_cpu_possible

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Date:   Tue, 18 May 2021 10:47:13 +0100
From:   Will Deacon <will@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...gle.com>, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, kernel-team@...roid.com
Subject: [PATCH v6 09/21] sched: Reject CPU affinity changes based on task_cpu_possible_mask()

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 task_cpu_possible_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.

Reviewed-by: Quentin Perret <qperret@...gle.com>
Signed-off-by: Will Deacon <will@...nel.org>
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 482f7fdca0e8..21da3d7f9e47 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2350,6 +2350,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 				  u32 flags)
 {
 	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;
@@ -2370,6 +2371,9 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 		 * set_cpus_allowed_common() and actually reset p->cpus_ptr.
 		 */
 		cpu_valid_mask = cpu_online_mask;
+	} else if (!cpumask_subset(new_mask, cpu_allowed_mask)) {
+		ret = -EINVAL;
+		goto out;
 	}
 
 	/*
-- 
2.31.1.751.gd2f1c929bd-goog