[Drbd-dev] Barrier assert failures with latest 8.0 sources

[Lars Ellenberg]

On Mon, Jan 21, 2008 at 09:29:02PM -0500, Graham, Simon wrote:
> > > I'm not sure why tl_clear leaves this pseudo-barrier in the list...
> > > shouldn't it simply leave the list completely empty just like
> tl_init
> > > does?
> > 
> > probably.
> > we have seen these ASSERTS, too, btw, also without this latest change
> > in
> > the barrier code, so aparently it has been there all along.
> > unfortunately we are all sort of distracted right now.
> > but coding will resume shortly :)
> 
> Well, I realize now that I completely misunderstood again;
> newest_barrier represents thenext barrier that will be sent, so of
> course there has to be one in the list at all times (and tl_init also
> sets up barrier 4711).
> 
> I think the problem is that tl_clear does NOT clear the CREATE_BARRIER
> bit from mdev->flags - so if we disconnect in the small window between
> setting this bit and creating the new barrier, then when we reconnect
> and send the first request, we'll end up creating a new barrier before
> sending the BarrierRq(4711) (processing the first request that has to go
> remote) and I think this gets us into the cycle of always being one
> barrier behind the remote system... this would also explain why the
> assert is intermittent since you have to disconnect in a small window...
> 
> Seem reasonable?

absolutely.

 :)

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