From: Clément Léger <cle...@rivosinc.com> [ Upstream commit 23cce5f25491968b23fb9c399bbfb25f13870cd9 ]
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 cond_resched() in trace_event_eval_update() allows other tasks to be executed and thus continue working asynchronously like before without blocking any pending task at boot time. Link: https://lore.kernel.org/linux-trace-kernel/20230929191637.416931-1-cle...@rivosinc.com Cc: Masami Hiramatsu <mhira...@kernel.org> Signed-off-by: Clément Léger <cle...@rivosinc.com> Tested-by: Atish Patra <ati...@rivosinc.com> Reviewed-by: Atish Patra <ati...@rivosinc.com> Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org> Signed-off-by: Sasha Levin <sas...@kernel.org> --- 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 37be6913cfb27..f29552b009c80 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -2240,6 +2240,7 @@ void trace_event_eval_update(struct trace_eval_map **map, int len) update_event_printk(call, map[i]); } } + cond_resched(); } up_write(&trace_event_sem); } -- 2.40.1
