4.19-stable review patch. If anyone has any objections, please let me know.
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From: Clément Léger cleger@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-cleger@ri...
Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Clément Léger cleger@rivosinc.com Tested-by: Atish Patra atishp@rivosinc.com Reviewed-by: Atish Patra atishp@rivosinc.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@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 a3dc6c126b3ee..ed39d3ec202e6 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -2242,6 +2242,7 @@ 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); }