On Tue, Oct 14, 2025 at 09:38:09AM +0200, Nam Cao wrote: > Thomas Weißschuh <[email protected]> writes: > > Reactors can be called from any context through tracepoints. > > When developing reactors care needs to be taken to only call APIs which > > are safe. As the tracepoints used during testing may not actually be > > called from restrictive contexts lockdep may not be helpful. > > > > Add explicit overrides to help lockdep find invalid code patterns. > > > > The usage of LD_WAIT_FREE will trigger lockdep warnings in the panic > > reactor. These are indeed valid warnings but they are out of scope for > > RV and will instead be fixed by the printk subsystem. > > > > Signed-off-by: Thomas Weißschuh <[email protected]> > > --- > ... > > void rv_react(struct rv_monitor *monitor, const char *msg, ...) > > { > > + static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map, LD_WAIT_FREE); > > va_list args; > > > > if (!rv_reacting_on() || !monitor->react) > > @@ -487,7 +489,9 @@ void rv_react(struct rv_monitor *monitor, const char > > *msg, ...) > > > > va_start(args, msg); > > > > + lock_map_acquire_try(&rv_react_map); > > monitor->react(msg, args); > > + lock_map_release(&rv_react_map); > > > > va_end(args); > > } > > The reactors are invoked in tracepoints' handlers, thus they must not > trigger another tracepoint, otherwise we may be stuck in an infinite loop. > (this is why preempt_enable_notrace() exists alongside preempt_enable()).
Sounds reasonable. However today not even the printk reactor satisfies this rule as it transitively calls trace_console(). > I'm not familiar with the internal lockdep. But I think these would > trigger trace_lock_acquire() and trace_lock_release(). Indeed. Right now no monitor attaches to those tracepoints. We could prevent monitors from attaching to certain "well-known" tracepoints. But then we still need to manually track which those are, which is ugly. Or we move the invocation of the reactor to a workqueue/task_work. Thomas
