sysrq: Properly check for kernel threads

There's a real possibility of killing kernel threads that might
have issued use_mm(), so kthread's mm might become non-NULL.

This patch fixes the issue by checking for PF_KTHREAD (just as
get_task_mm()).

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index a1bcad7..8db9125 100644 (file)
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -324,9 +324,12 @@ static void send_sig_all(int sig)
 
        read_lock(&tasklist_lock);
        for_each_process(p) {
-               if (p->mm && !is_global_init(p))
-                       /* Not swapper, init nor kernel thread */
-                       force_sig(sig, p);
+               if (p->flags & PF_KTHREAD)
+                       continue;
+               if (is_global_init(p))
+                       continue;
+
+               force_sig(sig, p);
        }
        read_unlock(&tasklist_lock);
 }