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>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index a1bcad7ef739..8db9125133b8 100644
--- 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);
 }