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ANDROID: cgroup/cpuset: Do not access task_cs(p) outside of RCU

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task_cs(p) is protected by RCU, so ensure that we have entered an RCU
read-side critical section before accessing it in guarantee_online_cpus().

This issue was introduced by 4045a05f88 ("BACKPORT: FROMLIST: cpuset:
Honour task_cpu_possible_mask() in guarantee_online_cpus()") and spotted
during upstream review.

Reported-by: Qais Yousef <qais.yousef@arm.com>
Link: https://lore.kernel.org/r/20210521162524.22cwmrao3df7m4jb@e107158-lin.cambridge.arm.com
Fixes: 4045a05f88 ("BACKPORT: FROMLIST: cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()")
Bug: 178507149
Change-Id: Ia8b8b89b5fcf72eefe9c2667951e24f315176ed5
Signed-off-by: Will Deacon <willdeacon@google.com>
This commit is contained in:
Will Deacon
2021-06-03 12:03:56 +01:00
parent 1099a4407d
commit 71b39cf2e5
1 changed files with 8 additions and 2 deletions
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10
kernel/cgroup/cpuset.c
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@@ -378,12 +378,15 @@ static inline bool is_in_v2_mode(void)
static void guarantee_online_cpus(struct task_struct *tsk, static void guarantee_online_cpus(struct task_struct *tsk,
struct cpumask *pmask) struct cpumask *pmask)
{ {
struct cpuset *cs = task_cs(tsk);
const struct cpumask *possible_mask = task_cpu_possible_mask(tsk); const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
struct cpuset *cs;
if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_active_mask))) if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_active_mask)))
cpumask_copy(pmask, cpu_active_mask); cpumask_copy(pmask, cpu_active_mask);
rcu_read_lock();
cs = task_cs(tsk);
while (!cpumask_intersects(cs->effective_cpus, pmask)) { while (!cpumask_intersects(cs->effective_cpus, pmask)) {
cs = parent_cs(cs); cs = parent_cs(cs);
if (unlikely(!cs)) { if (unlikely(!cs)) {
@@ -394,10 +397,13 @@ static void guarantee_online_cpus(struct task_struct *tsk,
* cpuset's effective_cpus is on its way to be * cpuset's effective_cpus is on its way to be
* identical to cpu_online_mask. * identical to cpu_online_mask.
*/ */
return; goto out_unlock;
} }
} }
cpumask_and(pmask, pmask, cs->effective_cpus); cpumask_and(pmask, pmask, cs->effective_cpus);
out_unlock:
rcu_read_unlock();
} }
/* /*