The patch titled
Subject: sched: check tgid in is_global_init
has been added to the -mm tree. Its filename is
sched-check-tgid-in-is_global_init.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/sched-check-tgid-in-is_global_init.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/sched-check-tgid-in-is_global_init.patch
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------------------------------------------------------
From: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Subject: sched: check tgid in is_global_init
Global init 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.
Link: https://www.redhat.com/archives/linux-audit/2013-December/msg00086.html
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Suggested-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN include/linux/sched.h~sched-check-tgid-in-is_global_init include/linux/sched.h
--- a/include/linux/sched.h~sched-check-tgid-in-is_global_init
+++ a/include/linux/sched.h
@@ -2013,7 +2013,8 @@ static inline int pid_alive(const struct
}
/**
- * 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.
@@ -2022,7 +2023,7 @@ static inline int pid_alive(const struct
*/
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;
_
Patches currently in -mm which might be from sergey.senozhatsky@xxxxxxxxx are
zram-zcomp-use-gfp_noio-to-allocate-streams.patch
zram-zcomp-do-not-zero-out-zcomp-private-pages.patch
printk-change-recursion_bug-type-to-bool.patch
sched-check-tgid-in-is_global_init.patch
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