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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 <peterz@infradead.org> Signed-off-by: Peilin He<he.peilin@zte.com.cn> Signed-off-by: xu xin <xu.xin16@zte.com.cn> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Yunkai Zhang <zhang.yunkai@zte.com.cn> Reviewed-by: Qiang Tu <tu.qiang35@zte.com.cn> Reviewed-by: Kun Jiang <jiang.kun2@zte.com.cn> Reviewed-by: Fan Yu <fan.yu9@zte.com.cn> Link: https://lkml.kernel.org/r/20240716104244764N2jD8gnBpnsLjCDnQGQ8c@zte.com.cn
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@ -2233,6 +2233,12 @@ void migrate_disable(void)
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struct task_struct *p = current;
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if (p->migration_disabled) {
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#ifdef CONFIG_DEBUG_PREEMPT
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/*
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*Warn about overflow half-way through the range.
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*/
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WARN_ON_ONCE((s16)p->migration_disabled < 0);
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#endif
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p->migration_disabled++;
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return;
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}
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@ -2251,14 +2257,20 @@ void migrate_enable(void)
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.flags = SCA_MIGRATE_ENABLE,
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};
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#ifdef CONFIG_DEBUG_PREEMPT
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/*
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* Check both overflow from migrate_disable() and superfluous
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* migrate_enable().
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*/
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if (WARN_ON_ONCE((s16)p->migration_disabled <= 0))
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return;
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#endif
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if (p->migration_disabled > 1) {
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p->migration_disabled--;
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return;
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}
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if (WARN_ON_ONCE(!p->migration_disabled))
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return;
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/*
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* Ensure stop_task runs either before or after this, and that
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* __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule().
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