On 2023-10-30 13:48, Christian König wrote:
Am 30.10.23 um 18:38 schrieb Felix Kuehling:
On 2023-10-30 12:16, Christian König wrote:
@@ -1904,6 +1906,19 @@ kfd_process_gpuid_from_node(struct
kfd_process *p, struct kfd_node *node,
return -EINVAL;
}
+static void signal_eviction_fence(struct kfd_process *p)
+{
+ spin_lock(&p->ef_lock);
+ if (!p->ef)
+ goto unlock_out;
+ dma_fence_signal(p->ef);
This needs to grab the internal lock of the eviction fence, I'm
not sure that has correct ordering with the newly added ef_lock.
Hmm, the only thing we could get a circular lock dependency would
be, if we took the p->ef_lock in a fence callback. I don't think
that ever happens, because even the eviction work runs on a worker
thread (exactly to avoid such lock dependency issues).
Anyway, I could try to move the fence_signal out of the critical
section. The lock is only there to ensure that exactly one process
signals and frees the fence.
So basically either the eviction worker or the GPU reset could
signal this fence.
In that case I think it would be simpler to grab the reset lock in
the eviction worker to protect against a concurrent reset.
Which reset lock? adev->reset_cntl->reset_lock? I only see that lock
taken in aldebaran_mode2_perform_reset. I don't understand why this
is in ASIC-specific code. But even so, it's only taken during the
actual reset (in aldebaran_mode2_perform_reset). I don't think it
covers the pre-reset code path that signals the eviction fence.
No, what I mean is adev->reset_domain->sem. It's hold in write lock
during the reset and you can grab the read side if you need to delay a
reset.
But thinking about that a bit more, you actually don't need any of
this. Something like this here should do fine:
tmp = dma_fence_get_rcu_safe(&p->ef);
dma_fence_signal(tmp);
dma_fence_put(tmp);
dma_fence_get_rcu_safe gets a new reference that dma_fence_put drops. It
doesn't drop the original reference in p->ef.
I need a way to ensure that exactly one thread frees the original
reference in p->ef. Even with RCU, concurrent writers still need a lock
or a mutex. So I don't think I can avoid using another lock here because
I have potentially two concurrent writers.
Regards,
Felix
dma_fences are always RCU protected and can be signaled from multiple
sources by design.
Regards,
Christian.
Regards,
Felix
Regards,
Christian.
