Commit acb6258a authored by Jiunn Chang's avatar Jiunn Chang Committed by Jonathan Corbet

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
......@@ -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,
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment