sched_show_task: fix unsafe usage of ->real_parent
rcu_read_lock() can not protect p->real_parent if release_task(p) was already called, change sched_show_task() to check pis_alive() like other users do. Note: we need some helpers to cleanup the code like this. And it seems that that the usage of cpu_curr(cpu) in dump_cpu_task() is not safe too. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Aaron Tomlin <atomlin@redhat.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Cc: Sterling Alexander <stalexan@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Roland McGrath <roland@hack.frob.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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