rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits
The current documentation did not help someone grepping for SRCU to
learn that disabling preemption is not a replacement for srcu_read_lock(),
so upgrade the documentation to bring this out, not just for SRCU,
but also for RCU-bh. Also document the fact that SRCU readers are
respected on CPUs executing in user mode, idle CPUs, and even on
offline CPUs.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index fc103d7..cdb20d4 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -310,6 +310,12 @@
code under the influence of preempt_disable(), you instead
need to use synchronize_irq() or synchronize_sched().
+ This same limitation also applies to synchronize_rcu_bh()
+ and synchronize_srcu(), as well as to the asynchronous and
+ expedited forms of the three primitives, namely call_rcu(),
+ call_rcu_bh(), call_srcu(), synchronize_rcu_expedited(),
+ synchronize_rcu_bh_expedited(), and synchronize_srcu_expedited().
+
12. Any lock acquired by an RCU callback must be acquired elsewhere
with softirq disabled, e.g., via spin_lock_irqsave(),
spin_lock_bh(), etc. Failing to disable irq on a given