From: Wen Yang <[email protected]>
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 <[email protected]>
Signed-off-by: Wen Yang <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
---
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
