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>
1093a9bfdb