cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace_stop()

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@gmail.com>
Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index c4da1ef56fdf..bcd46f547db3 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2205,8 +2205,8 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t
                  */
                 preempt_disable();
                 read_unlock(&tasklist_lock);
-                preempt_enable_no_resched();
                 cgroup_enter_frozen();
+                preempt_enable_no_resched();
                 freezable_schedule();
                 cgroup_leave_frozen(true);
         } else {