GEM - radeon cs ioctl deadlock

Thomas Hellstrom thomas at
Mon Oct 18 08:16:07 PDT 2010

On 10/14/2010 03:47 AM, Ben Skeggs wrote:
> On Thu, 2010-10-14 at 08:14 +1000, Dave Airlie wrote:
>> On Wed, 2010-10-13 at 17:57 -0400, Jerome Glisse wrote:
>>> So we are facing a deadlock with the radeon cs ioctl. When a buffer is given
>>> a name (with flink) we could endup with 2 handle pointing to the same
>>> object (flink object and open it from same file descriptor). Would it be ok
>>> if i change gem open to first look if we already have an handle for the
>>> object and to use that handle instead of creating a new one ? Or could
>>> this break intel driver ?
>> I think r300g worked around this already, maybe we should just avoid
>> doing it from userspace if possible.
> We had this in nouveau at some point.  In the end, I prevented the
> deadlock from occuring by checking that a process doesn't reserve the
> same buffer twice (we store file_priv in a reserved_by field in the bo
> as we reserve the buffers), and then just fixed userspace.
> Ben.
Hi, Ben,

Without knowing the exact details, that sounds a little dangerous? It 
would be better to use a process identifier rather than a file 
identifier since multiple threads in a single client can and should use 
the same file descriptor.


>> Dave.
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