Re: [PATCH] perf/core: Add SRCU annotation for pmus list walk

[Peter Zijlstra]

On Tue, Nov 19, 2019 at 01:14:29PM +0100, Sebastian Andrzej Siewior wrote:
> Since commit
>    28875945ba98d ("rcu: Add support for consolidated-RCU reader checking")
> 
> there is an additional check to ensure that a RCU related lock is held
> while the RCU list is iterated.
> This section holds the SRCU reader lock instead.
> 
> Add annotation to list_for_each_entry_rcu() that pmus_srcu must be
> acquired during the list traversal.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> 
> I see the warning in in v5.4-rc during boot. For some reason I don't see
> it in tip/master during boot but "perf stat w" triggers it again (among
> other things).
> 
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5224388872069..dbb3b26a55612 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10497,7 +10497,7 @@ static struct pmu *perf_init_event(struct perf_event *event)
>  		goto unlock;
>  	}
>  
> -	list_for_each_entry_rcu(pmu, &pmus, entry) {
> +	list_for_each_entry_rcu(pmu, &pmus, entry, lockdep_is_held(&pmus_srcu)) {

That's a bit obnoxious, but ok, I suppose.