[PATCH v3 1/4] rv/reactors: use context-sensitive lockdep wait type in rv_react()

[wen.yang@linux.dev]

From: Wen Yang <wen.yang@linux.dev>

Reactors must not explicitly take locks, so they should comply with
LD_WAIT_FREE.  However, reactor callbacks can run with preemption
enabled on any kernel (not just PREEMPT_RT).  If a timer interrupt
fires during the callback, the interrupt exit path schedules and
acquires rq->__lock (LD_WAIT_SPIN) while the lockdep override map that
declared LD_WAIT_FREE is still held, triggering a spurious
"Invalid wait context" warning:

    [ BUG: Invalid wait context ]
    context-{5:5}
    1 lock held by kunit_try_catch/209:
     #0: (rv_react_map-wait-type-override){+.+.}-{1:1}
    kunit_try_catch/209 is trying to lock:
    ffff8a743ed3e8a0 (&rq->__lock){-...}-{2:2}

Fixes: 69d8895cb9a9 ("rv: Add explicit lockdep context for reactors")
Suggested-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Wen Yang <wen.yang@linux.dev>
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 kernel/trace/rv/rv_reactors.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/rv/rv_reactors.c b/kernel/trace/rv/rv_reactors.c
index 2f5fc8d18dea..5830229210e8 100644
--- a/kernel/trace/rv/rv_reactors.c
+++ b/kernel/trace/rv/rv_reactors.c
@@ -465,18 +465,28 @@ int init_rv_reactors(struct dentry *root_dir)
 
 void rv_react(struct rv_monitor *monitor, const char *msg, ...)
 {
-	static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map, LD_WAIT_FREE);
+	/*
+	 * Reactors must not explicitly take locks, so they should be
+	 * LD_WAIT_FREE.  However, reactor callbacks can run with preemption
+	 * enabled, meaning the preempting code (e.g. the scheduler taking
+	 * rq->__lock at LD_WAIT_SPIN) may violate that constraint.  Use
+	 * LD_WAIT_SPIN in preemptible contexts to avoid false-positive lockdep
+	 * reports; keep LD_WAIT_FREE in NMI/hardirq where preemption is
+	 * disabled and the scheduler cannot run.
+	 */
+	static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map,        LD_WAIT_SPIN);
+	static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map_atomic, LD_WAIT_FREE);
+	struct lockdep_map * __maybe_unused map;
 	va_list args;
 
 	if (!rv_reacting_on() || !monitor->react)
 		return;
 
+	map = (in_nmi() || in_hardirq()) ? &rv_react_map_atomic : &rv_react_map;
 	va_start(args, msg);
-
-	lock_map_acquire_try(&rv_react_map);
+	lock_map_acquire_try(map);
 	monitor->react(msg, args);
-	lock_map_release(&rv_react_map);
-
+	lock_map_release(map);
 	va_end(args);
 }
 EXPORT_SYMBOL_GPL(rv_react);
-- 
2.25.1