Re: [PATCH v2 0/7] xfree86: Handle drm race condition

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

Op 20-03-13 09:40, Maarten Lankhorst schreef:
> Hey,
>
> Op 19-03-13 22:13, Chris Wilson schreef:
>> On Tue, Mar 19, 2013 at 11:50:47AM +0100, Maarten Lankhorst wrote:
>>> The drmSetMaster call is needed, but the spinning is really just waiting for the workqueue to run.
>>>
>>> bryce's patch never worked, it just caused it to try drmsetinterfaceversion for a few seconds before timing out. That call
>>> was failing because his patch series never tried to obtain drm master.
>> You missed that the series Bryce posted did contain the drmSetMaster()
>> call inside the loop to retry drmSetVersion(). :)
>>
>>
> Oh I must have missed that.
>
> Is the drmSetInterfaceVersion call really needed here? If I look at DRM_IOCTL_GET_UNIQUE,
> I don't see any requirement of drm master or anything, so it looks to me like for this specific race
> the drmSetInterfaceVersion call can be skipped entirely without any side effects.
> This would end up with cleaner code here, and drop the master requirement entirely.
>
> Of course there's still a race that needs to be investigated, and is currently not completely understood, I think.
>
Or worse, is that drmGetBusId call there even useful? From digging at the kernel it seems it's a per master value.
So if a device is hotplugged, it wouldn't be set yet. If someone else holds master, it wouldn't be set either.
In fact it would only be ever set from DRIOpenDRMMaster, but that call only happens a lot later, if it even happens at all.

It seems to me like opening the fd there should be removed entirely, and the bus id should be retrieved from the udev event instead.

I'll try to get something working for this.

~Maarten