From: Wen Yang <[email protected]>
rv_react() overrides the lockdep wait type to LD_WAIT_FREE to enforce
that reactor callbacks take no locks. But callbacks run in the context
of the triggering tracepoint, which can be preemptible task context on
any kernel. A timer interrupt firing during the callback makes the
interrupt-exit path schedule and take rq->__lock (LD_WAIT_SPIN) while
the LD_WAIT_FREE override is still held, producing 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 LD_WAIT_SPIN instead of LD_WAIT_FREE, which causes false-positive
warnings in preemptible contexts due to scheduler preemption taking
rq->__lock. Add documentation to runtime-verification.rst.
Fixes: 69d8895cb9a9 ("rv: Add explicit lockdep context for reactors")
Reviewed-by: Gabriele Monaco <[email protected]>
Signed-off-by: Wen Yang <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
---
kernel/trace/rv/rv_reactors.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/rv/rv_reactors.c b/kernel/trace/rv/rv_reactors.c
index 2f5fc8d18dea..ff7d478227c3 100644
--- a/kernel/trace/rv/rv_reactors.c
+++ b/kernel/trace/rv/rv_reactors.c
@@ -465,7 +465,15 @@ 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 to avoid false-positive lockdep reports.
+ * But you should still NOT be using locks in reactors.
+ */
+ static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map, LD_WAIT_SPIN);
va_list args;
if (!rv_reacting_on() || !monitor->react)
--
2.25.1
