From: Clément Léger Date: Fri, 29 Sep 2023 19:16:37 +0000 (+0200) Subject: tracing: relax trace_event_eval_update() execution with cond_resched() X-Git-Tag: v5.15.137~59 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=59ebfeb7b319b0a942e09ddf3c7c6e11c8de7db3;p=thirdparty%2Fkernel%2Fstable.git tracing: relax trace_event_eval_update() execution with cond_resched() [ 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-cleger@rivosinc.com Cc: Masami Hiramatsu Signed-off-by: Clément Léger Tested-by: Atish Patra Reviewed-by: Atish Patra Signed-off-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin --- diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index c626d02776a54..f8af4a15c3a88 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -2753,6 +2753,7 @@ void trace_event_eval_update(struct trace_eval_map **map, int len) update_event_fields(call, map[i]); } } + cond_resched(); } up_write(&trace_event_sem); }