Re: [PATCH -next] drm/panfrost: Fix PM reference leak in panfrost_job_hw_submit()

From: Samuel Zou <zou_wei@huawei.com>
To: Steven Price <steven.price@arm.com>, <robh@kernel.org>,
	<tomeu.vizoso@collabora.com>, <airlied@linux.ie>,
	<daniel@ffwll.ch>, <alyssa.rosenzweig@collabora.com>
Cc: <dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -next] drm/panfrost: Fix PM reference leak in panfrost_job_hw_submit()
Date: Thu, 13 May 2021 10:07:09 +0800	[thread overview]
Message-ID: <be1d7a48-be86-3713-e623-61bbd08125f7@huawei.com> (raw)
In-Reply-To: <7ebf35ef-58c3-7bc7-f0e9-ad487bae6686@arm.com>

Hi Steven,

Thanks for your review and also answer my doubts. Looking forward to 
your patch.

On 2021/5/12 23:23, Steven Price wrote:
> On 11/05/2021 07:29, Zou Wei wrote:
>> pm_runtime_get_sync will increment pm usage counter even it failed.
>> Forgetting to putting operation will result in reference leak here.
>> Fix it by replacing it with pm_runtime_resume_and_get to keep usage
>> counter balanced.
>>
>> Reported-by: Hulk Robot <hulkci@huawei.com>
>> Signed-off-by: Zou Wei <zou_wei@huawei.com>
> 
> Thanks for the patch, but this is actually incorrect. 
> panfrost_job_hw_submit() is expected to unconditionally increment the pm 
> usage counter. This is because panfrost_job_hw_submit() can (currently) 
> never fail, so in this case the job is considered "submitted" (even 
> though it never reaches the hardware) and it's handled by the job timeout.
> 
> However this is at least the second time[1] this phantom "reference 
> leak" has been raised, so perhaps it's time to handle this better. I'll 
> post a patch reworking panfrost_job_hw_submit() so it can fail.
> 
> Thanks,
> 
> Steve
> 
> [1] 
> https://lore.kernel.org/r/20200520110504.24388-1-dinghao.liu%40zju.edu.cn
> 
>> ---
>>   drivers/gpu/drm/panfrost/panfrost_job.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c 
>> b/drivers/gpu/drm/panfrost/panfrost_job.c
>> index 6003cfe..42d8dbc 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
>> @@ -157,7 +157,7 @@ static void panfrost_job_hw_submit(struct 
>> panfrost_job *job, int js)
>>       panfrost_devfreq_record_busy(&pfdev->pfdevfreq);
>> -    ret = pm_runtime_get_sync(pfdev->dev);
>> +    ret = pm_runtime_resume_and_get(pfdev->dev);
>>       if (ret < 0)
>>           return;
>>
> 
> .