blob: 01e89d97ab0e1fad2cbfa7509b25e99a71e6bb22 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
|
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 3 Aug 2023 12:09:32 +0200
Subject: [PATCH 2/2] signal: Don't disable preemption in ptrace_stop() on
PREEMPT_RT.
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
On PREEMPT_RT keeping preemption disabled during the invocation of
cgroup_enter_frozen() is a problem because the function acquires css_set_lock
which is a sleeping lock on PREEMPT_RT and must not be acquired with disabled
preemption.
The preempt-disabled section is only for performance optimisation
reasons and can be avoided.
Extend the comment and don't disable preemption before scheduling on
PREEMPT_RT.
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20230803100932.325870-3-bigeasy@linutronix.de
---
kernel/signal.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2344,11 +2344,20 @@ static int ptrace_stop(int exit_code, in
* The preempt-disable section ensures that there will be no preemption
* between unlock and schedule() and so improving the performance since
* the ptracer has no reason to sleep.
+ *
+ * On PREEMPT_RT locking tasklist_lock does not disable preemption.
+ * Therefore the task can be preempted (after
+ * do_notify_parent_cldstop()) before unlocking tasklist_lock so there
+ * is no benefit in doing this. The optimisation is harmful on
+ * PEEMPT_RT because the spinlock_t (in cgroup_enter_frozen()) must not
+ * be acquired with disabled preemption.
*/
- preempt_disable();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
read_unlock(&tasklist_lock);
cgroup_enter_frozen();
- preempt_enable_no_resched();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable_no_resched();
schedule();
cgroup_leave_frozen(true);
|
