[PATCH v2 1/4] rv/reactors: use context-sensitive lockdep wait type in rv_react()

From: Wen Yang <[email protected]>

The single DEFINE_WAIT_OVERRIDE_MAP(rv_react_map, LD_WAIT_FREE) in
rv_react() declares wait_type_inner = LD_WAIT_FREE for every execution
context.  In a preemptible context (e.g. CONFIG_PREEMPT_RT or a KUnit
test running on a task), a timer interrupt can fire during a reactor
callback; the interrupt exit path then schedules and acquires rq->__lock
(LD_WAIT_SPIN) while the override map is still held.  Since the map
declares the context to be wait-free, lockdep reports 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}

Use two lockdep override maps, selected by execution context:

  - Preemptible context (task, softirq, PREEMPT_RT irq thread): the
    scheduler may preempt, so use LD_WAIT_SPIN, the tightest wait type
    the scheduler itself uses, to suppress the spurious warning.

  - NMI/hardirq context: preemption is disabled and the scheduler cannot
    run, so the false positive cannot arise.  Keep LD_WAIT_FREE here to
    preserve the original constraint that reactors must not take raw
    spinlocks in atomic context.

Fixes: 69d8895cb9a9 ("rv: Add explicit lockdep context for reactors")
Signed-off-by: Wen Yang <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
---
 kernel/trace/rv/rv_reactors.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/rv/rv_reactors.c b/kernel/trace/rv/rv_reactors.c
index 2f5fc8d18dea..cd571b1649f5 100644
--- a/kernel/trace/rv/rv_reactors.c
+++ b/kernel/trace/rv/rv_reactors.c
@@ -465,18 +465,25 @@ 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);
+	/*
+	 * A reactor callback can be preempted; the scheduler then takes
+	 * rq->__lock (LD_WAIT_SPIN).  Advertise that in preemptible contexts
+	 * to avoid a spurious lockdep report, and keep LD_WAIT_FREE in atomic
+	 * ones where 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