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SubjectRe: [PATCH] trace/osnoise: fix event unhooking
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Hi Nikita

On 12/28/21 15:07, Nikita Yushchenko wrote:
> If start_per_cpu_kthreads() called from osnoise_workload_start() returns
> error, event hooks are left in broken state: unhook_irq_events() called
> but unhook_thread_events() and unhook_softirq_events() not called, and
> trace_osnoise_callback_enabled flag not cleared.
>
> On the next tracer enable, hooks get not installed due to
> trace_osnoise_callback_enabled flag.
>
> And on the further tracer disable an attempt to remove non-installed
> hooks happened, hitting a WARN_ON_ONCE() in tracepoint_remove_func().
>
> Fix the error path by adding the missing part of cleanup.

Regarding the subject:

- use tracing/ as subsystem (yeah, I also made this mistake in the original
osnoise series).
- use a capital after the "tracing/osnoise:"

Using your subject as example, it should be:
tracing/osnoise: Fix event unhooking

Anyway, I suggest using something more precise, like:

tracing/osnoise: Properly unhook events if start_per_cpu_kthreads() fails

or something like that.

> While at this, introduce osnoise_unhook_events() to avoid code
> duplication between this error path and notmal tracer disable.

s/notmal/normal/

>
> Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
> Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
> ---
> kernel/trace/trace_osnoise.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
> index 7520d43aed55..aa6f26612ccc 100644
> --- a/kernel/trace/trace_osnoise.c
> +++ b/kernel/trace/trace_osnoise.c
> @@ -2123,6 +2123,13 @@ static int osnoise_hook_events(void)
> return -EINVAL;
> }
>
> +static void osnoise_unhook_events(void)
> +{
> + unhook_thread_events();
> + unhook_softirq_events();
> + unhook_irq_events();
> +}
> +
> /*
> * osnoise_workload_start - start the workload and hook to events
> */
> @@ -2155,7 +2162,8 @@ static int osnoise_workload_start(void)
>
> retval = start_per_cpu_kthreads();
> if (retval) {
> - unhook_irq_events();
> + trace_osnoise_callback_enabled = false;

we need a barrier here, like:

/*
* Make sure that ftrace_nmi_enter/exit() see
* trace_osnoise_callback_enabled as false before continuing.
*/
barrier();

> + osnoise_unhook_events();
> return retval;
> }
>

Thanks!

-- Daniel

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