Re: [PATCH] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections
From: Waiman Long <hidden>
Date: 2025-09-12 21:13:15
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cgroups, intel-gfx, linux-acpi, linux-fsdevel, linux-nfs, linux-rt-devel, linux-s390, linux-security-module, lkml
On 9/12/25 2:50 AM, pengdonglin wrote:
From: pengdonglin <redacted> 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