jffs2_garbage_collect_thread() can race with SIGCONT and sleep in
TASK_STOPPED state after it was already sent. Add the new helper,
kernel_signal_stop(), which does this correctly.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 fs/jffs2/background.c |  3 +--
 include/linux/sched.h | 10 ++++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/jffs2/background.c b/fs/jffs2/background.c
index f3145fd..53cc735 100644
--- a/fs/jffs2/background.c
+++ b/fs/jffs2/background.c
@@ -132,8 +132,7 @@ static int jffs2_garbage_collect_thread(void *_c)
 			case SIGSTOP:
 				jffs2_dbg(1, "%s(): SIGSTOP received\n",
 					  __func__);
-				set_current_state(TASK_STOPPED);
-				schedule();
+				kernel_signal_stop();
 				break;
 
 			case SIGKILL:
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e714539..56e688c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2477,6 +2477,16 @@ static inline int kernel_dequeue_signal(siginfo_t *info)
 	return ret;
 }
 
+static inline void kernel_signal_stop(void)
+{
+	spin_lock_irq(&current->sighand->siglock);
+	if (current->jobctl & JOBCTL_STOP_DEQUEUED)
+		__set_current_state(TASK_STOPPED);
+	spin_unlock_irq(&current->sighand->siglock);
+
+	schedule();
+}
+
 extern void release_task(struct task_struct * p);
 extern int send_sig_info(int, struct siginfo *, struct task_struct *);
 extern int force_sigsegv(int, struct task_struct *);
-- 
2.4.3