Re: [PATCH v2] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections
From: Waiman Long <hidden>
Date: 2025-09-15 14:13:36
Also in:
cgroups, intel-gfx, linux-acpi, linux-fsdevel, linux-nfs, linux-rt-devel, linux-s390, linux-security-module, lkml
On 9/15/25 9:47 AM, pengdonglin wrote:
From: pengdonglin <redacted> 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/ (local) [3] https://lwn.net/Articles/777036/ [4] https://lore.kernel.org/lkml/6435833a-bdcb-4114-b29d-28b7f436d47d@paulmck-laptop/ (local) Cc: Waiman Long <longman@redhat.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Hillf Danton <redacted> Cc: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: pengdonglin <redacted> Signed-off-by: pengdonglin <redacted> --- 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(-)
...
quoted hunk ↗ jump to hunk
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 <longman@redhat.com>