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From:   Will Deacon <will@kernel.org>
To:     linux-arm-kernel@lists.infradead.org
Cc:     linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        Will Deacon <will@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>,
        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>,
        kernel-team@android.com
Subject: [PATCH v4 11/14] sched: Reject CPU affinity changes based on arch_task_cpu_possible_mask()
Date:   Tue, 24 Nov 2020 15:50:36 +0000
Message-Id: <20201124155039.13804-12-will@kernel.org>
In-Reply-To: <20201124155039.13804-1-will@kernel.org>
References: <20201124155039.13804-1-will@kernel.org>
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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_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.

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 99992d0beb65..095deda50643 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_task_cpu_possible_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;
 	}
 
 	/*
-- 
2.29.2.454.gaff20da3a2-goog