On Fri, 29 Sep 2023 16:13:48 +0200 Clément Léger <cle...@rivosinc.com> wrote:
> When kernel is compiled without preemption, the eval_map_work_func() > (which calls trace_event_eval_update()) will not be preempted up to its > complete execution. This can actually cause a problem since if another > CPU call stop_machine(), the call will have to wait for the > eval_map_work_func() function to finish executing in the workqueue > before being able to be scheduled. This problem was observe on a SMP > system at boot time, when the CPU calling the initcalls executed > clocksource_done_booting() which in the end calls stop_machine(). We > observed a 1 second delay because one CPU was executing > eval_map_work_func() and was not preempted by the stop_machine() task. > > Adding a call to schedule() in trace_event_eval_update() allows to let > other tasks to be executed and thus continue working asynchronously like > before without blocking any pending task at boot time. > > Signed-off-by: Clément Léger <cle...@rivosinc.com> > --- > kernel/trace/trace_events.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 91951d038ba4..dbdf57a081c0 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -2770,6 +2770,7 @@ void trace_event_eval_update(struct trace_eval_map > **map, int len) > update_event_fields(call, map[i]); > } > } > + schedule(); The proper answer to this is "cond_resched()" but still, there's going to be work to get rid of all that soon [1]. But I'll take a cond_resched() now until that is implemented. -- Steve > } > up_write(&trace_event_sem); > } [1] https://lore.kernel.org/all/87cyyfxd4k.ffs@tglx/
