From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> In kernels built with CONFIG_PREEMPT_RT=n, spinlock critical sections are RCU readers because they disable preemption. However, they are also RCU readers in CONFIG_PREEMPT_RT=y because in that case the locking primitives contain rcu_read_lock() and rcu_read_unlock(). Therefore, upgrade checklist.rst to document this non-obvious case. While in the area, fix a typo by changing "read-side critical" to "read-side critical section". Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- Documentation/RCU/checklist.rst | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index 2d42998a89a6..98a622f77248 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -68,7 +68,8 @@ over a rather long period of time, but improvements are always welcome! rcu_read_lock_sched(), or by the appropriate update-side lock. Explicit disabling of preemption (preempt_disable(), for example) can serve as rcu_read_lock_sched(), but is less readable and - prevents lockdep from detecting locking issues. + prevents lockdep from detecting locking issues. Acquiring a + spinlock also enters an RCU read-side critical section. Please note that you *cannot* rely on code known to be built only in non-preemptible kernels. Such code can and will break, @@ -444,7 +445,7 @@ over a rather long period of time, but improvements are always welcome! real-time workloads than is synchronize_rcu_expedited(). It is also permissible to sleep in RCU Tasks Trace read-side - critical, which are delimited by rcu_read_lock_trace() and + critical section, which are delimited by rcu_read_lock_trace() and rcu_read_unlock_trace(). However, this is a specialized flavor of RCU, and you should not use it without first checking with its current users. In most cases, you should instead use SRCU. -- 2.43.0
