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 the -rt locking primitives contain rcu_read_lock() and rcu_read_unlock(). Therefore, upgrade rcu_dereference.rst to document this non-obvious case. Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Closes: https://lore.kernel.org/lkml/CAHk-=whGKvjHCtJ6W4pQ0_h_k9fiFQ8V2GpM=BqYnB2X=SJ+XQ@xxxxxxxxxxxxxx/ Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- Documentation/RCU/rcu_dereference.rst | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/Documentation/RCU/rcu_dereference.rst b/Documentation/RCU/rcu_dereference.rst index 659d5913784d..2524dcdadde2 100644 --- a/Documentation/RCU/rcu_dereference.rst +++ b/Documentation/RCU/rcu_dereference.rst @@ -408,7 +408,10 @@ member of the rcu_dereference() to use in various situations: RCU flavors, an RCU read-side critical section is entered using rcu_read_lock(), anything that disables bottom halves, anything that disables interrupts, or anything that disables - preemption. + preemption. Please note that spinlock critical sections + are also implied RCU read-side critical sections, even when + they are preemptible, as they are in kernels built with + CONFIG_PREEMPT_RT=y. 2. If the access might be within an RCU read-side critical section on the one hand, or protected by (say) my_lock on the other, -- 2.43.0
