rcu: Upgrade srcu_read_lock() docbook about SRCU grace periods
It is illegal to wait for an SRCU grace period while within the
corresponding flavor of SRCU read-side critical section. Therefore,
this commit updates the srcu_read_lock() docbook accordingly.
Signed-off-by: Paul E. McKenney <[email protected]>
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 6f456a7..58971e8 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -139,7 +139,12 @@
* @sp: srcu_struct in which to register the new reader.
*
* Enter an SRCU read-side critical section. Note that SRCU read-side
- * critical sections may be nested.
+ * critical sections may be nested. However, it is illegal to
+ * call anything that waits on an SRCU grace period for the same
+ * srcu_struct, whether directly or indirectly. Please note that
+ * one way to indirectly wait on an SRCU grace period is to acquire
+ * a mutex that is held elsewhere while calling synchronize_srcu() or
+ * synchronize_srcu_expedited().
*/
static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
{
