[tip: core/rcu] rcutorture: Don't do need_resched() testing if ->sync is NULL

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     a7eb937b67b64b8b4645f1ebca3ac2079c6de81b
Gitweb:        https://git.kernel.org/tip/a7eb937b67b64b8b4645f1ebca3ac2079c6de81b
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Fri, 09 Oct 2020 19:51:55 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Fri, 06 Nov 2020 17:13:57 -08:00

rcutorture: Don't do need_resched() testing if ->sync is NULL

If cur_ops->sync is NULL, rcu_torture_fwd_prog_nr() will nevertheless
attempt to call through it.  This commit therefore flags cases where
neither need_resched() nor call_rcu() forward-progress testing
can be performed due to NULL function pointers, and also causes
rcu_torture_fwd_prog_nr() to take an early exit if cur_ops->sync()
is NULL.

Reported-by: Tom Rix <trix@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/rcutorture.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index e7d52fd..4dfd113 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1923,7 +1923,9 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp,
 	unsigned long stopat;
 	static DEFINE_TORTURE_RANDOM(trs);
 
-	if  (cur_ops->call && cur_ops->sync && cur_ops->cb_barrier) {
+	if (!cur_ops->sync)
+		return; // Cannot do need_resched() forward progress testing without ->sync.
+	if (cur_ops->call && cur_ops->cb_barrier) {
 		init_rcu_head_on_stack(&fcs.rh);
 		selfpropcb = true;
 	}
@@ -2149,8 +2151,8 @@ static int __init rcu_torture_fwd_prog_init(void)
 
 	if (!fwd_progress)
 		return 0; /* Not requested, so don't do it. */
-	if (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0 ||
-	    cur_ops == &rcu_busted_ops) {
+	if ((!cur_ops->sync && !cur_ops->call) ||
+	    !cur_ops->stall_dur || cur_ops->stall_dur() <= 0 || cur_ops == &rcu_busted_ops) {
 		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
 		return 0;
 	}