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Commit acb6258a authored by Jiunn Chang's avatar Jiunn Chang Committed by Jonathan Corbet
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doc: RCU callback locks need only _bh, not necessarily _irq 



The UP.rst file calls for locks acquired within RCU callback functions
to use _irq variants (spin_lock_irqsave() or similar), which does work,
but can be overkill.  This commit therefore instead calls for _bh variants
(spin_lock_bh() or similar), while noting that _irq does work.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: default avatarJiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 62ee81b5

Documentation/RCU/UP.rst

+7 −6
Original line number Diff line number Diff line
@@ -113,12 +113,13 @@ Answer to Quick Quiz #1: 
Answer to Quick Quiz #2:

	What locking restriction must RCU callbacks respect?



	Any lock that is acquired within an RCU callback must be

	acquired elsewhere using an _irq variant of the spinlock

	primitive.  For example, if "mylock" is acquired by an

	RCU callback, then a process-context acquisition of this

	lock must use something like spin_lock_irqsave() to

	acquire the lock.

	Any lock that is acquired within an RCU callback must be acquired

	elsewhere using an _bh variant of the spinlock primitive.

	For example, if "mylock" is acquired by an RCU callback, then

	a process-context acquisition of this lock must use something

	like spin_lock_bh() to acquire the lock.  Please note that

	it is also OK to use _irq variants of spinlocks, for example,

	spin_lock_irqsave().



	If the process-context code were to simply use spin_lock(),

	then, since RCU callbacks can be invoked from softirq context,