Patch "tracing: relax trace_event_eval_update() execution with cond_resched()" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tracing: relax trace_event_eval_update() execution with cond_resched()

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-relax-trace_event_eval_update-execution-with.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d6f649ba7076f600f26de25b7302cf163c058d92
Author: Clément Léger <cleger@xxxxxxxxxxxx>
Date:   Fri Sep 29 21:16:37 2023 +0200

    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@xxxxxxxxxxxx
    
    Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
    Signed-off-by: Clément Léger <cleger@xxxxxxxxxxxx>
    Tested-by: Atish Patra <atishp@xxxxxxxxxxxx>
    Reviewed-by: Atish Patra <atishp@xxxxxxxxxxxx>
    Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 51adf0817ef3a..4f42dd0880796 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2236,6 +2236,7 @@ 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);
 }