Re: [PATCH] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections
Sebastian Andrzej Siewior <[email protected]>
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On 2025-09-12 17:13:09 [-0400], Waiman Long wrote: > On 9/12/25 2:50 AM, pengdonglin wrote: > > From: pengdonglin <[email protected]> > > > > 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. The claim is valid since Paul merged the three flavours we had. Before that preempt_disable() (and disabling irqs) would match rcu_read_lock_sched(). rcu_read_lock() and rcu_read_lock_bh() were different in terms of grace period and clean up. So _now_ we could remove it if it makes things easier. > Cheers, > Longman Sebastian