On Mon 2021-10-18 22:02:03, Steven Rostedt wrote:
> On Mon, 18 Oct 2021 12:19:20 +0200
> Petr Mladek <pmladek@xxxxxxxx> wrote:
>
> > > -
> > > bit = trace_get_context_bit() + start;
> > > if (unlikely(val & (1 << bit))) {
> > > /*
> > > * It could be that preempt_count has not been updated during
> > > * a switch between contexts. Allow for a single recursion.
> > > */
> > > - bit = TRACE_TRANSITION_BIT;
> > > + bit = TRACE_CTX_TRANSITION + start;
> >
>
> [..]
>
> > Could we please update the comment? I mean to say if it is a race
> > or if we trace a function that should not get traced.
>
> What do you think of this change?
>
> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
> index 1d8cce02c3fb..24f284eb55a7 100644
> --- a/include/linux/trace_recursion.h
> +++ b/include/linux/trace_recursion.h
> @@ -168,8 +168,12 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
> bit = trace_get_context_bit() + start;
> if (unlikely(val & (1 << bit))) {
> /*
> - * It could be that preempt_count has not been updated during
> - * a switch between contexts. Allow for a single recursion.
> + * If an interrupt occurs during a trace, and another trace
> + * happens in that interrupt but before the preempt_count is
> + * updated to reflect the new interrupt context, then this
> + * will think a recursion occurred, and the event will be dropped.
> + * Let a single instance happen via the TRANSITION_BIT to
> + * not drop those events.
> */
> bit = TRACE_TRANSITION_BIT;
> if (val & (1 << bit)) {
>
>
Looks good to me. Thanks for the update.
Feel free to postpone this change. I do not want to complicate
upstreaming the fix for stable. I am sorry if I already
complicated it.
Best Regards,
Petr
