linux-kernel - [PATCH 5.3 19/48] cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace

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Message-Id: <20191119051003.108253979@linuxfoundation.org>
Date:   Tue, 19 Nov 2019 06:19:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        Roman Gushchin <guro@...com>, Tejun Heo <tj@...nel.org>,
        Bruce Ashfield <bruce.ashfield@...il.com>
Subject: [PATCH 5.3 19/48] cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace_stop()

From: Oleg Nesterov <oleg@...hat.com>

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@...il.com>
Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
Cc: stable@...r.kernel.org # v5.2+
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Roman Gushchin <guro@...com>
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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 {