From: Waiman Long <llong@redhat.com>
To: pengdonglin <dolinux.peng@gmail.com>,
tj@kernel.org, tony.luck@intel.com, jani.nikula@linux.intel.com,
ap420073@gmail.com, jv@jvosburgh.net, freude@linux.ibm.com,
bcrl@kvack.org, trondmy@kernel.org, kees@kernel.org
Cc: bigeasy@linutronix.de, linux-kernel@vger.kernel.org,
linux-rt-devel@lists.linux.dev, linux-nfs@vger.kernel.org,
linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, netdev@vger.kernel.org,
intel-gfx@lists.freedesktop.org, linux-acpi@vger.kernel.org,
linux-s390@vger.kernel.org, cgroups@vger.kernel.org,
pengdonglin <pengdonglin@xiaomi.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections
Date: Fri, 12 Sep 2025 17:13:09 -0400 [thread overview]
Message-ID: <6831b9fe-402f-40a6-84e6-b723dd006b90@redhat.com> (raw)
In-Reply-To: <20250912065050.460718-1-dolinux.peng@gmail.com>
On 9/12/25 2:50 AM, pengdonglin wrote:
> From: pengdonglin <pengdonglin@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
next prev parent reply other threads:[~2025-09-12 21:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-12 6:50 [PATCH] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections pengdonglin
2025-09-12 21:13 ` Waiman Long [this message]
2025-09-12 21:35 ` Sebastian Andrzej Siewior
2025-09-13 0:33 ` Waiman Long
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