Commit 120311ac authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Boqun Feng
Browse files

doc: Spinlocks are implied RCU readers 



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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/lkml/CAHk-=whGKvjHCtJ6W4pQ0_h_k9fiFQ8V2GpM=BqYnB2X=SJ+XQ@mail.gmail.com/


Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
parent 41bccc98

Documentation/RCU/rcu_dereference.rst

+4 −1
Original line number Diff line number Diff line
@@ -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,