oom: avoid killing kthreads if they assume the oom killed thread's mm

After selecting a task to kill, the oom killer iterates all processes and
kills all other threads that share the same mm_struct in different thread
groups.  It would not otherwise be helpful to kill a thread if its memory
would not be subsequently freed.

A kernel thread, however, may assume a user thread's mm by using
use_mm().  This is only temporary and should not result in sending a
SIGKILL to that kthread.

This patch ensures that only user threads and not kthreads are sent a
SIGKILL if they share the same mm_struct as the oom killed task.

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d897262..b0d8943 100644 (file)
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -439,7 +439,7 @@ static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
        task_unlock(p);
 
        /*
        task_unlock(p);
 
        /*

-        * Kill all processes sharing p->mm in other thread groups, if any.
+        * Kill all user processes sharing p->mm in other thread groups, if any.

         * They don't get access to memory reserves or a higher scheduler
         * priority, though, to avoid depletion of all memory or task
         * starvation.  This prevents mm->mmap_sem livelock when an oom killed
         * They don't get access to memory reserves or a higher scheduler
         * priority, though, to avoid depletion of all memory or task
         * starvation.  This prevents mm->mmap_sem livelock when an oom killed


@@ -449,7 +449,8 @@ static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
         * signal.
         */
        for_each_process(q)
         * signal.
         */
        for_each_process(q)

-               if (q->mm == mm && !same_thread_group(q, p)) {
+               if (q->mm == mm && !same_thread_group(q, p) &&
+                   !(q->flags & PF_KTHREAD)) {

                        task_lock(q);   /* Protect ->comm from prctl() */
                        pr_err("Kill process %d (%s) sharing same memory\n",
                                task_pid_nr(q), q->comm);
                        task_lock(q);   /* Protect ->comm from prctl() */
                        pr_err("Kill process %d (%s) sharing same memory\n",
                                task_pid_nr(q), q->comm);