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From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: maarten.lankhorst@linux.intel.com, mripard@kernel.org,
	tzimmermann@suse.de, airlied@linux.ie, sumit.semwal@linaro.org,
	christian.koenig@amd.com, axboe@kernel.dk, oleg@redhat.com,
	tglx@linutronix.de, dvyukov@google.com,
	walter-zh.wu@mediatek.com, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
	skhan@linuxfoundation.org, gregkh@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master
Date: Wed, 18 Aug 2021 22:50:00 +0800	[thread overview]
Message-ID: <a69a6870-18fe-5bbc-074e-871753a8f593@gmail.com> (raw)
In-Reply-To: <YRzbTUM8ggXlIEyr@phenom.ffwll.local>

On 18/8/21 6:05 pm, Daniel Vetter wrote:
> On Wed, Aug 18, 2021 at 03:38:17PM +0800, Desmond Cheong Zhi Xi wrote:
>> When drm_file.master changes value, the corresponding
>> drm_device.master_lookup_lock should be held.
>>
>> In drm_master_release, a call to drm_master_put sets the
>> file_priv->master to NULL, so we protect this section with
>> drm_device.master_lookup_lock.
>>
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> 
> At this points all refcounts to drm_file have disappeared, so yeah this is
> a lockless access, but also no one can observe it anymore. See also next
> patch.
> 
> Hence I think the current code is fine.
> -Daniel
> 

Ah ok got it, I didn't realize that. I'll drop patch 2 and 3 from the 
series then.

>> ---
>>   drivers/gpu/drm/drm_auth.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
>> index 8efb58aa7d95..8c0e0dba1611 100644
>> --- a/drivers/gpu/drm/drm_auth.c
>> +++ b/drivers/gpu/drm/drm_auth.c
>> @@ -373,8 +373,11 @@ void drm_master_release(struct drm_file *file_priv)
>>   	}
>>   
>>   	/* drop the master reference held by the file priv */
>> -	if (file_priv->master)
>> +	if (file_priv->master) {
>> +		spin_lock(&dev->master_lookup_lock);
>>   		drm_master_put(&file_priv->master);
>> +		spin_unlock(&dev->master_lookup_lock);
>> +	}
>>   	mutex_unlock(&dev->master_mutex);
>>   }
>>   
>> -- 
>> 2.25.1
>>
> 


  reply	other threads:[~2021-08-18 14:50 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18  7:38 [PATCH v3 0/9] drm, kernel: update locking for DRM Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 1/9] drm: move master_lookup_lock into drm_device Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master Desmond Cheong Zhi Xi
2021-08-18 10:05   ` Daniel Vetter
2021-08-18 14:50     ` Desmond Cheong Zhi Xi [this message]
2021-08-18  7:38 ` [PATCH v3 3/9] drm: check for null master in drm_is_current_master_locked Desmond Cheong Zhi Xi
2021-08-18 10:04   ` Daniel Vetter
2021-08-18  7:38 ` [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth,ioctl} Desmond Cheong Zhi Xi
2021-08-18 10:11   ` Daniel Vetter
2021-08-18 15:37     ` Desmond Cheong Zhi Xi
2021-08-18 16:33       ` [Intel-gfx] [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth, ioctl} Daniel Vetter
2021-08-19  5:31         ` Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 5/9] drm: protect magic_map,unique{_len} with master_lookup_lock Desmond Cheong Zhi Xi
2021-08-18 10:43   ` Daniel Vetter
2021-08-18  7:38 ` [PATCH v3 6/9] drm: convert drm_device.master_mutex into a rwsem Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 7/9] drm: update global mutex lock in the ioctl handler Desmond Cheong Zhi Xi
2021-08-18 11:02   ` Daniel Vetter
2021-08-19 10:52     ` Desmond Cheong Zhi Xi
2021-08-19 11:21       ` [Intel-gfx] " Daniel Vetter
2021-08-18  7:38 ` [PATCH v3 8/9] kernel: export task_work_add Desmond Cheong Zhi Xi
2021-08-18 11:06   ` Daniel Vetter
2021-08-19  9:26   ` Christoph Hellwig
2021-08-19  9:40     ` Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 9/9] drm: avoid races with modesetting rights Desmond Cheong Zhi Xi

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