linux-kernel - [PATCH 08/18] rcu: Eliminate rcu_gp_slow

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Message-Id: <20231013115902.1059735-9-frederic@kernel.org>
Date:   Fri, 13 Oct 2023 13:58:52 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Neeraj Upadhyay <neeraj.upadhyay@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Uladzislau Rezki <urezki@...il.com>, rcu <rcu@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 08/18] rcu: Eliminate rcu_gp_slow_unregister() false positive

From: "Paul E. McKenney" <paulmck@...nel.org>

When using rcutorture as a module, there are a number of conditions that
can abort the modprobe operation, for example, when attempting to run
both RCU CPU stall warning tests and forward-progress tests.  This can
cause rcu_torture_cleanup() to be invoked on the unwind path out of
rcu_rcu_torture_init(), which will mean that rcu_gp_slow_unregister()
is invoked without a matching rcu_gp_slow_register().  This will cause
a splat because rcu_gp_slow_unregister() is passed rcu_fwd_cb_nodelay,
which does not match a NULL pointer.

This commit therefore forgives a mismatch involving a NULL pointer, thus
avoiding this false-positive splat.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index aae515071ffd..a83ecab77917 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1260,7 +1260,7 @@ EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
 /* Unregister a counter, with NULL for not caring which. */
 void rcu_gp_slow_unregister(atomic_t *rgssp)
 {
-	WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
+	WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL);

 	WRITE_ONCE(rcu_gp_slow_suppress, NULL);
 }
-- 
2.34.1