rcu: Pull out wait_event*() condition into helper function
The condition for the wait_event_interruptible_timeout() that waits
to do the next force-quiescent-state scan is a bit ornate:
((gf = READ_ONCE(rsp->gp_flags)) &
RCU_GP_FLAG_FQS) ||
(!READ_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp))
This commit therefore pulls this condition out into a helper function
and comments its component conditions.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4b6594c..b280373 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1904,6 +1904,26 @@
}
/*
+ * Helper function for wait_event_interruptible_timeout() wakeup
+ * at force-quiescent-state time.
+ */
+static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
+{
+ struct rcu_node *rnp = rcu_get_root(rsp);
+
+ /* Someone like call_rcu() requested a force-quiescent-state scan. */
+ *gfp = READ_ONCE(rsp->gp_flags);
+ if (*gfp & RCU_GP_FLAG_FQS)
+ return true;
+
+ /* The current grace period has completed. */
+ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
+ return true;
+
+ return false;
+}
+
+/*
* Do one round of quiescent-state forcing.
*/
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
@@ -2067,11 +2087,7 @@
TPS("fqswait"));
rsp->gp_state = RCU_GP_WAIT_FQS;
ret = wait_event_interruptible_timeout(rsp->gp_wq,
- ((gf = READ_ONCE(rsp->gp_flags)) &
- RCU_GP_FLAG_FQS) ||
- (!READ_ONCE(rnp->qsmask) &&
- !rcu_preempt_blocked_readers_cgp(rnp)),
- j);
+ rcu_gp_fqs_check_wake(rsp, &gf), j);
rsp->gp_state = RCU_GP_DONE_FQS;
/* Locking provides needed memory barriers. */
/* If grace period done, leave loop. */