Commit 234a503e authored by Will Deacon's avatar Will Deacon Committed by Peter Zijlstra
Browse files

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.

Signed-off-by: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: default avatarQuentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210730112443.23245-6-will@kernel.org
parent 97c0054d

kernel/sched/core.c

+8 −1
Original line number Diff line number Diff line
@@ -2709,7 +2709,9 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, 
				  const struct cpumask *new_mask,

				  u32 flags)

{

	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);

	const struct cpumask *cpu_valid_mask = cpu_active_mask;

	bool kthread = p->flags & PF_KTHREAD;

	unsigned int dest_cpu;

	struct rq_flags rf;

	struct rq *rq;
@@ -2718,7 +2720,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, 
	rq = task_rq_lock(p, &rf);

	update_rq_clock(rq);



	if (p->flags & PF_KTHREAD || is_migration_disabled(p)) {

	if (kthread || is_migration_disabled(p)) {

		/*

		 * Kernel threads are allowed on online && !active CPUs,

		 * however, during cpu-hot-unplug, even these might get pushed
@@ -2732,6 +2734,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, 
		cpu_valid_mask = cpu_online_mask;

	}



	if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {

		ret = -EINVAL;

		goto out;

	}



	/*

	 * Must re-check here, to close a race against __kthread_bind(),

	 * sched_setaffinity() is not guaranteed to observe the flag.