linux-kernel - Re: [PATCH] perf: fixing variable initialisation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <87k2tkbzo6.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Tue, 28 Jul 2015 08:48:25 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>,
	a.p.zijlstra@...llo.nl, mingo@...hat.com, acme@...nel.org
Cc:	linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org
Subject: Re: [PATCH] perf: fixing variable initialisation

Mathieu Poirier <mathieu.poirier@...aro.org> writes:

> Variable 'max_order' needs to be initialised to log2 of the
> number of pages invariant of the no scather-gather PMU option.
> Otherwise 'rb_alloc_aux_page' gets an order that is equal to
> '0', which prevents the private page information to be set
> properly.

But that wouldn't make sense: we're only using the private field in
pages at the bottom of high-order allocations, which only ever happen
for NO_SG devices. Otherwise, every page is the buffer is just an
individual page and doesn't need anything in the private field.

> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> ---
>  kernel/events/ring_buffer.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 96472824a752..bd3da7bebe9e 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -449,18 +449,18 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
>  {
>  	bool overwrite = !(flags & RING_BUFFER_WRITABLE);
>  	int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
> -	int ret = -ENOMEM, max_order = 0;
> +	int ret = -ENOMEM, max_order;
>  
>  	if (!has_aux(event))
>  		return -ENOTSUPP;
>  
> -	if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
> -		/*
> -		 * We need to start with the max_order that fits in nr_pages,
> -		 * not the other way around, hence ilog2() and not get_order.
> -		 */
> -		max_order = ilog2(nr_pages);
> +	/*
> +	 * We need to start with the max_order that fits in nr_pages,
> +	 * not the other way around, hence ilog2() and not get_order.
> +	 */
> +	max_order = ilog2(nr_pages);

Also, nr_pages here is the whole buffer, but when we do use
page::private, we put an each individual high-order allocation's order
there, not the whole buffer's, which makes sense because you'd need to
know the former to program the HW properly, whereas the latter you'd get
as a parameter to pmu::setup_aux() callback anyway.

Regards,
--
Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/