[PATCH] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections

[Waiman Long]

On 9/12/25 2:50 AM, pengdonglin wrote:
> From: pengdonglin <pengdonglin at xiaomi.com>
>
> When CONFIG_PREEMPT_RT is disabled, spin_lock*() operations implicitly
> disable preemption, which provides RCU read-side protection. When
> CONFIG_PREEMPT_RT is enabled, spin_lock*() implementations internally
> manage RCU read-side critical sections.

I have some doubt about your claim that disabling preemption provides 
RCU read-side protection. It is true for some flavors but probably not 
all. I do know that disabling interrupt will provide RCU read-side 
protection. So for spin_lock_irq*() calls, that is valid. I am not sure 
about spin_lock_bh(), maybe it applies there too. we need some RCU 
people to confirm.

When CONFIG_PREEMPT_RT is enabled, rt_spin_lock/unlock() will call 
rcu_read_lock/_unlock() internally. So eliminating explicit 
rcu_read_lock/unlock() in critical sections should be fine.

Cheers,
Longman