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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-78903aec245sm7995186d6.23.2025.09.15.07.13.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Sep 2025 07:13:27 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <69af79b6-a4f2-4007-aef4-fcaeeadd3f99@redhat.com> Date: Mon, 15 Sep 2025 10:13:26 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections To: pengdonglin , 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, Hillf Danton , "Paul E . McKenney" , pengdonglin References: <20250915134729.1801557-1-dolinux.peng@gmail.com> Content-Language: en-US In-Reply-To: <20250915134729.1801557-1-dolinux.peng@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/15/25 9:47 AM, pengdonglin wrote: > From: pengdonglin > > Per Documentation/RCU/rcu_dereference.rst [1], since Linux 4.20's RCU > consolidation [2][3], RCU read-side critical sections include: > - Explicit rcu_read_lock() > - BH/interrupt/preemption-disabling regions > - Spinlock critical sections (including CONFIG_PREEMPT_RT kernels [4]) > > Thus, explicit rcu_read_lock()/unlock() calls within spin_lock*() regions are redundant. > This patch removes them, simplifying locking semantics while preserving RCU protection. > > [1] https://elixir.bootlin.com/linux/v6.17-rc5/source/Documentation/RCU/rcu_dereference.rst#L407 > [2] https://lore.kernel.org/lkml/20180829222021.GA29944@linux.vnet.ibm.com/ > [3] https://lwn.net/Articles/777036/ > [4] https://lore.kernel.org/lkml/6435833a-bdcb-4114-b29d-28b7f436d47d@paulmck-laptop/ > > Cc: Waiman Long > Cc: Sebastian Andrzej Siewior > Cc: Hillf Danton > Cc: Paul E. McKenney > Signed-off-by: pengdonglin > Signed-off-by: pengdonglin > --- > Changes in v2: > - Clarified commit message to prevent accidental backport to older kernels > - Added lockdep_is_held() to avoid false positives > --- > drivers/acpi/apei/ghes.c | 2 -- > drivers/gpu/drm/i915/gt/intel_ring_submission.c | 2 -- > drivers/net/amt.c | 8 -------- > drivers/net/bonding/bond_3ad.c | 2 -- > drivers/net/wireless/ath/ath9k/xmit.c | 2 -- > drivers/s390/crypto/pkey_base.c | 3 --- > fs/aio.c | 6 ++---- > fs/nfs/callback_proc.c | 2 -- > fs/nfs/nfs4state.c | 2 -- > fs/nfs/pnfs.c | 9 --------- > fs/nfs/pnfs_dev.c | 4 ---- > ipc/msg.c | 1 - > ipc/sem.c | 1 - > ipc/shm.c | 1 - > ipc/util.c | 2 -- > kernel/cgroup/cgroup.c | 2 -- > kernel/cgroup/cpuset.c | 6 ------ > kernel/cgroup/debug.c | 4 ---- > net/mac80211/cfg.c | 2 -- > net/mac80211/debugfs.c | 2 -- > net/mac80211/debugfs_netdev.c | 2 -- > net/mac80211/debugfs_sta.c | 2 -- > net/mac80211/sta_info.c | 2 -- > net/ncsi/ncsi-manage.c | 2 -- > security/yama/yama_lsm.c | 4 ---- > 25 files changed, 2 insertions(+), 73 deletions(-) >  ... > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 27adb04df675..9b7e8e8e9411 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -4073,7 +4073,6 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > struct cpuset *cs; > > spin_lock_irqsave(&callback_lock, flags); > - rcu_read_lock(); > > cs = task_cs(tsk); > if (cs != &top_cpuset) > @@ -4095,7 +4094,6 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > cpumask_copy(pmask, possible_mask); > } > > - rcu_read_unlock(); > spin_unlock_irqrestore(&callback_lock, flags); > } > > @@ -4168,9 +4166,7 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk) > unsigned long flags; > > spin_lock_irqsave(&callback_lock, flags); > - rcu_read_lock(); > guarantee_online_mems(task_cs(tsk), &mask); > - rcu_read_unlock(); > spin_unlock_irqrestore(&callback_lock, flags); > > return mask; > @@ -4265,10 +4261,8 @@ bool cpuset_current_node_allowed(int node, gfp_t gfp_mask) > /* Not hardwall and node outside mems_allowed: scan up cpusets */ > spin_lock_irqsave(&callback_lock, flags); > > - rcu_read_lock(); > cs = nearest_hardwall_ancestor(task_cs(current)); > allowed = node_isset(node, cs->mems_allowed); > - rcu_read_unlock(); > > spin_unlock_irqrestore(&callback_lock, flags); > return allowed; For cpuset, Acked-by: Waiman Long