[dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nikos Tsironis]

On 3/9/22 10:51, Mikulas Patocka wrote:
> 
> Hi
> 
> Note that you must submit kcopyd callbacks from a single thread, otherwise
> there's a race condition in snapshot.
> 

Hi,

Thanks for the feedback. Yes, I'm aware of that.

> The snapshot code doesn't take locks in the copy_callback and it expects
> that the callbacks are serialized.
> 
> Maybe, adding the locks to copy_callback would solve it.
> 

That's what I did. I used a lock to ensure that kcopyd callbacks are
serialized for persistent snapshots.

For transient snapshots we can lift this limitation, and complete
pending exceptions out-of-oder and in "parallel", i.e., without
explicitly serializing kcopyd callbacks. The locks in pending_complete()
are enough in this case.

Nikos