Am 17.10.2016 um 20:02 schrieb Rob Clark:
On Mon, Oct 17, 2016 at 4:25 AM, Maarten Lankhorst
<maarten.lankhorst@xxxxxxxxxxxxxxx> wrote:
Op 16-10-16 om 18:03 schreef Rob Clark:
Currently with fence-array, we have a potential deadlock situation. If we
fence_add_callback() on an array-fence, the array-fence's lock is aquired
first, and in it's ->enable_signaling() callback, it will install cb's on
it's array-member fences, so the array-member's lock is acquired second.
But in the signal path, the array-member's lock is acquired first, and the
array-fence's lock acquired second.
One approach to deal with this is avoid holding the fence's lock when
calling the cb. It is a bit intrusive and I haven't fixed up all the
other drivers that call directly or indirectly fence_signal_locked().
I guess the other option would be introduce a work-queue for array-fence?
Or??
Enable signaling when creating the fence array is an option. As an optimization we don't enable
signaling when creating a single fence, but when you merge fences you're probably interested
in the result anyway.
I think what you mean is to fence_add_callback() on all the member
fences up-front, rather from ops->enable_signaling()? I guess that
should work.
Yeah, but we should try to avoid that. Enabling signaling all the time
is really expensive for some use cases.
I would certainly prefer the approach using a work item.
Regards,
Christian.
BR,
-R
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