[PATCH linux-next] sched/core: Add WARN() to checks in migrate_disable()
From: xu.xin16
Date: Fri Jun 28 2024 - 01:06:11 EST
From: Peilin He <he.peilin@xxxxxxxxxx>
Background
==========
When repeated migrate_disable() calls are made with missing
the corresponding migrate_enable() calls, there is a risk of
'migration_disabled' going upper overflow because
'migration_disabled' is a type of unsigned short whose max
value is 65535.
In PREEMPT_RT kernel, if 'migration_disabled' goes upper
overflow, it may make the migrate_disable() ineffective
within local_lock_irqsave(). This is because, during the
scheduling procedure, the value of 'migration_disabled' will be
checked, which can trigger CPU migration. Consequently,
the count of 'rcu_read_lock_nesting' may leak due to
local_lock_irqsave() and local_unlock_irqrestore() occurring on
different CPUs.
Usecase
========
For example, When I developed a driver, I encountered
a "WARNING: CPU: 4 PID: 260 at kernel/rcu/tree_plugin.h:315
rcu_note_context_switch+0xa8/0x4e8" warning. It took me
half a month to locate this issue. Ultimately, I discovered
that the lack of upper overflow detection mechanism in
migrate_disable() was the root cause, leading to a significant
amount of time spent on problem localization.
If the upper overflow detection mechanism was added to
migrate_disable(), the root cause could be very quickly and
easily identified.
Effect
======
Using WARN() to check if 'migration_disabled' is upper overflow
can help developers quickly identify the issue.
Signed-off-by: Peilin He<he.peilin@xxxxxxxxxx>
Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
Reviewed-by: Yunkai Zhang <zhang.yunkai@xxxxxxxxxx>
Reviewed-by: Qiang Tu <tu.qiang35@xxxxxxxxxx>
Reviewed-by: Kun Jiang <jiang.kun2@xxxxxxxxxx>
Reviewed-by: Fan Yu <fan.yu9@xxxxxxxxxx>
Cc: Yang Yang <yang.yang29@xxxxxxxxxx>
Cc: Liu Chun <liu.chun2@xxxxxxxxxx>
---
kernel/sched/core.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8cc4975d6b2b..14671291564c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2259,6 +2259,8 @@ void migrate_disable(void)
struct task_struct *p = current;
if (p->migration_disabled) {
+ if (p->migration_disabled == USHRT_MAX)
+ WARN(1, "migration_disabled has encountered an overflow.\n");
p->migration_disabled++;
return;
}
--
2.17.1