Commit 8dbc33b4 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Boqun Feng
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doc: Make whatisRCU.rst note that spinlocks are 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 in that case the locking
primitives contain rcu_read_lock() and rcu_read_unlock().  Therefore,
upgrade whatisRCU.rst to document this non-obvious case.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
parent 120311ac

Documentation/RCU/whatisRCU.rst

+13 −2
Original line number Diff line number Diff line
@@ -172,14 +172,25 @@ rcu_read_lock() 
	critical section.  Reference counts may be used in conjunction

	with RCU to maintain longer-term references to data structures.



	Note that anything that disables bottom halves, preemption,

	or interrupts also enters an RCU read-side critical section.

	Acquiring a spinlock also enters an RCU read-side critical

	sections, even for spinlocks that do not disable preemption,

	as is the case in kernels built with CONFIG_PREEMPT_RT=y.

	Sleeplocks do *not* enter RCU read-side critical sections.



rcu_read_unlock()

^^^^^^^^^^^^^^^^^

	void rcu_read_unlock(void);



	This temporal primitives is used by a reader to inform the

	reclaimer that the reader is exiting an RCU read-side critical

	section.  Note that RCU read-side critical sections may be nested

	and/or overlapping.

	section.  Anything that enables bottom halves, preemption,

	or interrupts also exits an RCU read-side critical section.

	Releasing a spinlock also exits an RCU read-side critical section.



	Note that RCU read-side critical sections may be nested and/or

	overlapping.



synchronize_rcu()

^^^^^^^^^^^^^^^^^