From 570f52412ae9432c56897472791ea8db420cbaf1 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Fri, 1 Jan 2016 23:03:01 +0900 Subject: [PATCH] sched/core: Check tgid in is_global_init() Our global init task can have sub-threads, so ->pid check is not reliable enough for is_global_init(), we need to check tgid instead. This has been spotted by Oleg and a fix was proposed by Richard a long time ago (see the link below). Oleg wrote: : Because is_global_init() is only true for the main thread of /sbin/init. : : Just look at oom_unkillable_task(). It tries to not kill init. But, say, : select_bad_process() can happily find a sub-thread of is_global_init() : and still kill it. I recently hit the problem in question; re-sending the patch (to the best of my knowledge it has never been submitted) with updated function comment. Credit goes to Oleg and Richard. Suggested-by: Richard Guy Briggs Reported-by: Oleg Nesterov Signed-off-by: Sergey Senozhatsky Signed-off-by: Peter Zijlstra (Intel) Acked-by: Serge Hallyn Cc: Andrew Morton Cc: Eric W . Biederman Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Serge E . Hallyn Cc: Sergey Senozhatsky Cc: Thomas Gleixner Link: https://www.redhat.com/archives/linux-audit/2013-December/msg00086.html Signed-off-by: Ingo Molnar --- include/linux/sched.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index edad7a4..9cf9dd1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2002,7 +2002,8 @@ static inline int pid_alive(const struct task_struct *p) } /** - * is_global_init - check if a task structure is init + * is_global_init - check if a task structure is init. Since init + * is free to have sub-threads we need to check tgid. * @tsk: Task structure to be checked. * * Check if a task structure is the first user space task the kernel created. @@ -2011,7 +2012,7 @@ static inline int pid_alive(const struct task_struct *p) */ static inline int is_global_init(struct task_struct *tsk) { - return tsk->pid == 1; + return task_tgid_nr(tsk) == 1; } extern struct pid *cad_pid; -- 2.7.4