Subject: Re: [PATCH] events: always do slow path when trying to find a pmu

From: Tejun Heo <[email-masked]>
Date: Wed, 20 Feb 2013 09:16:45 -0800

On Wed, Feb 20, 2013 at 07:09:36PM +0200, Andy Shevchenko wrote:
> The guilty commit is cc5b5f6 "events: convert to idr_alloc()" together with
> f49318a "idr: implement lookup hint". In our case the idr_alloc is never called, but idr_find is. The hint field is never initialized and could not be dereferenced.

Ah, right, ->hint is uninitialized at the beginning.

> The proposed fix uses the idr_slowpath call which reflects old behaviour.
> 
> Signed-off-by: Andy Shevchenko <[email-masked]>
> Reported-by: Kirill A. Shutemov <[email-masked]>
> ---
>  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 624e53f..20421ea 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6076,7 +6076,7 @@ struct pmu *perf_init_event(struct perf_event *event)
>  	idx = srcu_read_lock(&pmus_srcu);
>  
>  	rcu_read_lock();
> -	pmu = idr_find(&pmu_idr, event->attr.type);
> +	pmu = idr_find_slowpath(&pmu_idr, event->attr.type);

But I don't think this is the right thing to do.  I'm working on
proper fix for idr_find().  Will post soon.

Thanks!

-- 
tejun