sysrq should grab the tasklist lock, otherwise calling force_sig() is
not safe, as it might race with exiting task, which ->sighand might be
set to NULL already.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 drivers/tty/sysrq.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 7867b7c..a1bcad7 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -322,11 +322,13 @@ static void send_sig_all(int sig)
 {
 	struct task_struct *p;
 
+	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);
 	}
+	read_unlock(&tasklist_lock);
 }
 
 static void sysrq_handle_term(int key)
-- 
1.7.7.6