linux-kernel - Re: [PATCH] drm/panfrost: fix ref count leak in panfrost_job_hw

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Message-ID: <30c2031a-4975-43d0-c8ca-8664969e5df3@arm.com>
Date:   Thu, 9 Jul 2020 16:59:13 +0100
From:   Steven Price <steven.price@....com>
To:     Rob Herring <robh@...nel.org>,
        Navid Emamdoost <navid.emamdoost@...il.com>
Cc:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Navid Emamdoost <emamd001@....edu>, wu000273@....edu,
        kjlu@....edu, Stephen McCamant <smccaman@....edu>
Subject: Re: [PATCH] drm/panfrost: fix ref count leak in
 panfrost_job_hw_submit

On 09/07/2020 16:44, Rob Herring wrote:
> On Sun, Jun 14, 2020 at 12:27 AM Navid Emamdoost
> <navid.emamdoost@...il.com> wrote:
>>
>> in panfrost_job_hw_submit, pm_runtime_get_sync is called which
>> increments the counter even in case of failure, leading to incorrect
>> ref count. In case of failure, decrement the ref count before returning.
>>
>> Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
>> ---
>>   drivers/gpu/drm/panfrost/panfrost_job.c | 8 +++++---
>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
>> index 7914b1570841..89ac84667eb1 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
>> @@ -147,11 +147,10 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>>
>>          ret = pm_runtime_get_sync(pfdev->dev);
>>          if (ret < 0)
>> -               return;
>> +               goto out;
> 
> If the get failed, I don't think we want to do a put.

The pm_runtime_get_sync() does actually always increment the reference 
(even when returning a failure), but actually I don't think we want it 
here anyway, as I think I explained before[1].
  [1] 
https://lore.kernel.org/dri-devel/272650ba-2c44-9084-7829-b04023eba723@arm.com
> 
>>
>>          if (WARN_ON(job_read(pfdev, JS_COMMAND_NEXT(js)))) {
>> -               pm_runtime_put_sync_autosuspend(pfdev->dev);

This is a correct change - we don't want the put here. (Although this 
should never happen).

>> -               return;
>> +               goto out;
>>          }
>>
>>          cfg = panfrost_mmu_as_get(pfdev, &job->file_priv->mmu);
>> @@ -184,6 +183,9 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>>                                  job, js, jc_head);
>>
>>          job_write(pfdev, JS_COMMAND_NEXT(js), JS_COMMAND_START);
> 
> So we start the job here and then...
> 
>> +out:
>> +       pm_runtime_put_sync_autosuspend(pfdev->dev);
> 
> ...turn off clocks/power here. Typically, you'd be fine as autosuspend
> has a delay by default, but userspace is free to change the delay to
> 0.
> 
>> +       return;

A return at the end of the function with no argument is pointless.

Steve

>>   }
>>
>>   static void panfrost_acquire_object_fences(struct drm_gem_object **bos,
>> --
>> 2.17.1
>>