sched/core: Add WARN_ON_ONCE() to check overflow for migrate_disable()

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 like
"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_ON_ONCE() to check if 'migration_disabled' is upper overflow
can help developers identify the issue quickly.

Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Peilin He<[email protected]>
Signed-off-by: xu xin <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Yunkai Zhang <[email protected]>
Reviewed-by: Qiang Tu <[email protected]>
Reviewed-by: Kun Jiang <[email protected]>
Reviewed-by: Fan Yu <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

0 files changed, 0 insertions, 0 deletions