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sched, cpuset: Fix dl_cpu_busy() panic due to empty cs->cpus_allowed

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With cgroup v2, the cpuset's cpus_allowed mask can be empty indicating
that the cpuset will just use the effective CPUs of its parent. So
cpuset_can_attach() can call task_can_attach() with an empty mask.
This can lead to cpumask_any_and() returns nr_cpu_ids causing the call
to dl_bw_of() to crash due to percpu value access of an out of bound
CPU value. For example:

	[80468.182258] BUG: unable to handle page fault for address: ffffffff8b6648b0
	  :
	[80468.191019] RIP: 0010:dl_cpu_busy+0x30/0x2b0
	  :
	[80468.207946] Call Trace:
	[80468.208947]  cpuset_can_attach+0xa0/0x140
	[80468.209953]  cgroup_migrate_execute+0x8c/0x490
	[80468.210931]  cgroup_update_dfl_csses+0x254/0x270
	[80468.211898]  cgroup_subtree_control_write+0x322/0x400
	[80468.212854]  kernfs_fop_write_iter+0x11c/0x1b0
	[80468.213777]  new_sync_write+0x11f/0x1b0
	[80468.214689]  vfs_write+0x1eb/0x280
	[80468.215592]  ksys_write+0x5f/0xe0
	[80468.216463]  do_syscall_64+0x5c/0x80
	[80468.224287]  entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix that by using effective_cpus instead. For cgroup v1, effective_cpus
is the same as cpus_allowed. For v2, effective_cpus is the real cpumask
to be used by tasks within the cpuset anyway.

Also update task_can_attach()'s 2nd argument name to cs_effective_cpus to
reflect the change. In addition, a check is added to task_can_attach()
to guard against the possibility that cpumask_any_and() may return a
value >= nr_cpu_ids.

Fixes: 7f51412a41 ("sched/deadline: Fix bandwidth check/update when migrating tasks between exclusive cpusets")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20220803015451.2219567-1-longman@redhat.com
This commit is contained in:
Waiman Long 2022-08-02 21:54:51 -04:00 committed by Ingo Molnar
parent 9de1f9c8ca
commit b6e8d40d43
3 changed files with 7 additions and 5 deletions
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2
include/linux/sched.h
View File

@ -1813,7 +1813,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
}
extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed);
extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
#ifdef CONFIG_SMP
extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);

2
kernel/cgroup/cpuset.c
View File

@ -2239,7 +2239,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
goto out_unlock;
cgroup_taskset_for_each(task, css, tset) {
ret = task_can_attach(task, cs->cpus_allowed);
ret = task_can_attach(task, cs->effective_cpus);
if (ret)
goto out_unlock;
ret = security_task_setscheduler(task);

8
kernel/sched/core.c
View File

@ -8980,7 +8980,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
}
int task_can_attach(struct task_struct *p,
const struct cpumask *cs_cpus_allowed)
const struct cpumask *cs_effective_cpus)
{
int ret = 0;
@ -8999,9 +8999,11 @@ int task_can_attach(struct task_struct *p,
}
if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
cs_cpus_allowed)) {
int cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed);
cs_effective_cpus)) {
int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);
if (unlikely(cpu >= nr_cpu_ids))
return -EINVAL;
ret = dl_cpu_busy(cpu, p);
}