[for-next][PATCH 02/34] srcu: Add notrace variant of srcu_dereference

From: Steven Rostedt
Date: Sat Aug 11 2018 - 09:53:14 EST

From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>

In the last patch in this series, we are making lockdep register hooks
onto the irq_{disable,enable} tracepoints. These tracepoints use the
_rcuidle tracepoint variant. In this series we switch the _rcuidle
tracepoint callers to use SRCU instead of sched-RCU. Inorder to
dereference the pointer to the probe functions, we could call
srcu_dereference, however this API will call back into lockdep to check
if the lock is held *before* the lockdep probe hooks have a chance to
run and annotate the IRQ enabled/disabled state.

For this reason we need a notrace variant of srcu_dereference since
otherwise we get lockdep splats. This patch adds the needed
srcu_dereference_notrace variant.

Link: http://lkml.kernel.org/r/20180628182149.226164-3-joel@xxxxxxxxxxxxxxxxx

Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
include/linux/srcu.h | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 3e72a291c401..67135d4a8a30 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -169,6 +169,11 @@ static inline int srcu_read_lock_held(const struct srcu_struct *sp)
#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)

+ * srcu_dereference_notrace - no tracing and no lockdep calls from here
+ */
+#define srcu_dereference_notrace(p, sp) srcu_dereference_check((p), (sp), 1)
* srcu_read_lock - register a new reader for an SRCU-protected structure.
* @sp: srcu_struct in which to register the new reader.