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

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Date:   Tue, 17 Dec 2019 13:21:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] perf/core: Add SRCU annotation for pmus list walk

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@...utronix.de>
> ---
> 
> 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.