[PATCH tip/core/rcu 4/4] srcu: Introduce srcu_read_{un,}lock_notrace()

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Joel Fernandes is using SRCU to protect from-idle tracepoints, which
requires notrace variants of srcu_read_lock() and srcu_read_unlock()
in order to avoid problems with tracepoints in lockdep.  This commit
therefore adds srcu_read_lock_notrace() and srcu_read_unlock_notrace().

[1] http://lkml.kernel.org/r/20180427042656.190746-1-joelaf@google.com

Reported-by: Joel Fernandes <joelaf@google.com>
Intermittently-reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 91494d7e8e41..3e72a291c401 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -195,6 +195,16 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 	return retval;
 }
 
+/* Used by tracing, cannot be traced and cannot invoke lockdep. */
+static inline notrace int
+srcu_read_lock_notrace(struct srcu_struct *sp) __acquires(sp)
+{
+	int retval;
+
+	retval = __srcu_read_lock(sp);
+	return retval;
+}
+
 /**
  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
  * @sp: srcu_struct in which to unregister the old reader.
@@ -209,6 +219,13 @@ static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 	__srcu_read_unlock(sp, idx);
 }
 
+/* Used by tracing, cannot be traced and cannot call lockdep. */
+static inline notrace void
+srcu_read_unlock_notrace(struct srcu_struct *sp, int idx) __releases(sp)
+{
+	__srcu_read_unlock(sp, idx);
+}
+
 /**
  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
  *
-- 
2.17.1