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sched: Reject CPU affinity changes based on task_cpu_possible_mask()

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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 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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210730112443.23245-6-will@kernel.org
This commit is contained in:
Will Deacon 2021-07-30 12:24:32 +01:00 committed by Peter Zijlstra
parent 97c0054dbe
commit 234a503e67
1 changed files with 8 additions and 1 deletions
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9
kernel/sched/core.c
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@ -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.