Commit-ID: 570f52412ae9432c56897472791ea8db420cbaf1
Gitweb: http://git.kernel.org/tip/570f52412ae9432c56897472791ea8db420cbaf1
Author: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
AuthorDate: Fri, 1 Jan 2016 23:03:01 +0900
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 6 Jan 2016 11:01:06 +0100
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 <rgb@xxxxxxxxxx>
Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Eric W . Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Serge E . Hallyn <serge.hallyn@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://www.redhat.com/archives/linux-audit/2013-December/msg00086.html
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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;
--
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