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Message-ID: <db60bb1d-51b6-6830-5a4c-100ba38a2dbc@linux.intel.com>
Date:   Tue, 17 Jan 2023 16:25:09 +0000
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Subject: Re: [RFC 04/12] drm/cgroup: Track clients per owning process
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To:     Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Cc:     Intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        Rob Clark <robdclark@chromium.org>,
        Brian Welty <brian.welty@intel.com>, Kenny.Ho@amd.com,
        Tvrtko Ursulin <tvrtko.ursulin@intel.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Johannes Weiner <hannes@cmpxchg.org>,
        linux-kernel@vger.kernel.org,
        =?UTF-8?Q?St=c3=a9phane_Marchesin?= <marcheu@chromium.org>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Zefan Li <lizefan.x@bytedance.com>,
        Dave Airlie <airlied@redhat.com>, Tejun Heo <tj@kernel.org>,
        cgroups@vger.kernel.org, "T . J . Mercier" <tjmercier@google.com>
References: <20230112165609.1083270-1-tvrtko.ursulin@linux.intel.com>
 <20230112165609.1083270-5-tvrtko.ursulin@linux.intel.com>
 <20230117160311.GA15842@linux.intel.com>
From:   Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Organization: Intel Corporation UK Plc
In-Reply-To: <20230117160311.GA15842@linux.intel.com>
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On 17/01/2023 16:03, Stanislaw Gruszka wrote:
> Hi
> 
> On Thu, Jan 12, 2023 at 04:56:01PM +0000, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> To enable propagation of settings from the cgroup drm controller to drm we
>> need to start tracking which processes own which drm clients.
>>
>> Implement that by tracking the struct pid pointer of the owning process in
>> a new XArray, pointing to a structure containing a list of associated
>> struct drm_file pointers.
>>
>> Clients are added and removed under the filelist mutex and RCU list
>> operations are used below it to allow for lockless lookup.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> <snip>
> 
>> +int drm_clients_open(struct drm_file *file_priv)
>> +{
>> +	struct drm_device *dev = file_priv->minor->dev;
>> +	struct drm_pid_clients *clients;
>> +	bool new_client = false;
>> +	unsigned long pid;
>> +
>> +	lockdep_assert_held(&dev->filelist_mutex);
>> +
>> +	pid = (unsigned long)rcu_access_pointer(file_priv->pid);
>> +	clients = xa_load(&drm_pid_clients, pid);
>> +	if (!clients) {
>> +		clients = __alloc_clients();
>> +		if (!clients)
>> +			return -ENOMEM;
>> +		new_client = true;
>> +	}
>> +	atomic_inc(&clients->num);
>> +	list_add_tail_rcu(&file_priv->clink, &clients->file_list);
>> +	if (new_client) {
>> +		void *xret;
>> +
>> +		xret = xa_store(&drm_pid_clients, pid, clients, GFP_KERNEL);
>> +		if (xa_err(xret)) {
>> +			list_del_init(&file_priv->clink);
>> +			kfree(clients);
>> +			return PTR_ERR(clients);
> 
> This looks incorrect, rather xa_err(xret) should be returned.

Thanks, looks like a copy & paste error. Noted to correct before next 
public post.

Regards,

Tvrtko