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ANDROID: sched: select fallback rq must check for allowed cpus

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select_fallback_rq() must return a cpu that is valid for the task.
However, when nid is not -1, it skips checking for
task_cpu_possible_mask().

This causes a problem when execve-ing 32 bit apps on an asymmetric
system where not all cpus are 32 bit capable. During execve-ing
the task is marked as 32 bit long before its affinity mask is
restricted.

If the cpu goes offline during this time, select_fallback_rq()
could return a 64 bit only cpu, which __migrate_tasks()/
is_cpu_allowed() rejects.

migrate_tasks() will therefore continue to pick the same task
repeatedly, where __migrate_tasks() rejects the cpu chosen
by select_fallback_rq() every time, leading to an infinite loop.

Correct the issue by updating select_fallback_rq() for the case
where nid is not -1, ensuring that the returned cpu is always
valid for this task.

Bug: 192050156
Change-Id: Ia073a8395a02485f6d1c1daa0f3ce9e2029cb1f4
Signed-off-by: Stephen Dickey <dickey@codeaurora.org>
This commit is contained in:
Stephen Dickey
2021-06-25 18:31:30 -07:00
committed by Will Deacon
parent 8943a2e7a3
commit 1093a9bfdb
1 changed files with 1 additions and 3 deletions
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4
kernel/sched/core.c
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@@ -2482,9 +2482,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
/* Look for allowed, online CPU in same node. */
for_each_cpu(dest_cpu, nodemask) {
if (!cpu_active(dest_cpu))
continue;
if (cpumask_test_cpu(dest_cpu, p->cpus_ptr))
if (is_cpu_allowed(p, dest_cpu))
return dest_cpu;
}
}