Re: [RFC][PATCH 3/3][cr][v2]: fileleases: C/R of an in-progress lease.

[Oren Laadan <orenl@cs.columbia.edu>]

On 05/25/2010 09:07 PM, Sukadev Bhattiprolu wrote:
> If process P1 has a F_WRLCK lease on file F1 and process P2 opens the
> file, P2's open() blocks for lease_break_time (45 seconds) and P1 gets
> a SIGIO to cleanup it lease in preparation for P2's open.  If the two
> processes are checkpointed/restarted in this window, we should address
> following two issues:
> 
> 	- P1 should get a SIGIO only once for the lease (i.e if P1 got the
> 	  SIGIO before checkpoint, it should not get the SIGIO after restart).

The qualification "before" is vague in our case - a checkpoint is
potentially a length operation, so before *which part* of the
checkpoint you mean here ?

> 
> 	- If R seconds remain in the lease, P2's open should be blocked for
> 	  at least the R seconds, so P1 has the time to clean up its lease.
> 	  The previous patch gives P1 the entire lease_break_time but that
> 	  can leave P2 stalled for 2*lease_break_time.
> 
> To address first, we add a field ->fl_break_notified to "remember" if we
> notified the lease-holder already. We save this field in the checkpoint
> image and when restarting, we notify the lease-holder only if this field
> is not set.

I'm not sure I understand.

Signals are saved last, in particular they are saved after files, and
file leases. What happens if we at checkpoint, we look at a file lease -
we save the least_break_time, now we proceed with the checkpoint, now
the lease expires before we are done, so we get a signal, and finally
we save the signals. In this case, we get both an expiry time and the
signal recorded.

(Am I mis-reading the code ?)

It seems to me that we need to mark the file lease at checkpoint to
prevent the signal from being sent until _after_ the checkpoint ends
(as opposed to remembering that the signal was sent). And then at the
end of the checkpoint, iterate through the leases for each marked
lease - remove the mark and fire the signal.

Oren.