[PATCH 5.3 19/48] cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace_stop()

[Greg Kroah-Hartman]

From: Oleg Nesterov <oleg@xxxxxxxxxx>

commit 937c6b27c73e02cd4114f95f5c37ba2c29fadba1 upstream.

ptrace_stop() does preempt_enable_no_resched() to avoid the preemption,
but after that cgroup_enter_frozen() does spin_lock/unlock and this adds
another preemption point.

Reported-and-tested-by: Bruce Ashfield <bruce.ashfield@xxxxxxxxx>
Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
Cc: stable@xxxxxxxxxxxxxxx # v5.2+
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/signal.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2205,8 +2205,8 @@ static void ptrace_stop(int exit_code, i
 		 */
 		preempt_disable();
 		read_unlock(&tasklist_lock);
-		preempt_enable_no_resched();
 		cgroup_enter_frozen();
+		preempt_enable_no_resched();
 		freezable_schedule();
 		cgroup_leave_frozen(true);
 	} else {