doc: Call out queue_rcu_work() for blocking RCU callbacks

The current checklist.rst file correctly notes that RCU callbacks execute
in BH context, and cannot block.  This commit adds words advising people
needing callbacks to block to use workqueues, for example, by replacing
call_rcu() with queue_rcu_work().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
index 5eedef027d922a64a75636ee2f0ff54191410df2..2db206fc3465f17f97786b57ff6853b95c0c9f1d 100644 (file)
--- a/Documentation/RCU/checklist.rst
+++ b/Documentation/RCU/checklist.rst
@@ -190,6 +190,9 @@ over a rather long period of time, but improvements are always welcome!
 
 5.     If call_rcu() or call_srcu() is used, the callback function will
        be called from softirq context.  In particular, it cannot block.
+       If you need the callback to block, run that code in a workqueue
+       handler scheduled from the callback.  The queue_rcu_work()
+       function does this for you in the case of call_rcu().
 
 6.     Since synchronize_rcu() can block, it cannot be called
        from any sort of irq context.  The same rule applies