Re: [dm-devel] Re: [PATCH 3/3] Add timeout feature

[Takashi Sato]

Hi Alasdair, Eric and Dave,

> On Thu, Jul 03, 2008 at 01:47:10PM +0100, Alasdair G Kergon wrote:
> > On Thu, Jul 03, 2008 at 09:11:05PM +0900, Takashi Sato wrote:
> > > If the freezer accesses the frozen filesystem and causes a deadlock,
> > > the above ideas can't solve it
> >
> > But you could also say that if the 'freezer' process accesses the frozen
> > filesystem and deadlocks then that's just a bug and that userspace code
> > should be fixed and there's no need to introduce the complexity of a
> > timeout parameter.
>
> Seconded - that was also my primary objection to the timeout code.

I will consider removing the timeout.

> > The point I'm trying to make here is:
> >   Under what real-world circumstances might multiple concurrent freezing
> >   attempts occur, and which of A, B or C (or other variations) would be
> >   the most appropriate way of handling such situations?
> >
> > A common example is people running xfs_freeze followed by an lvm command
> > which also attempts to freeze the filesystem.
>
> Yes, I've seen that reported a number of times.
>
> > I can see a case for B or C, but personally I prefer A:
> >
> > > > 1 succeeds, freezes
> > > > 2 succeeds, remains frozen
> > > > 3 succeeds, remains frozen
> > > > 4 succeeds, thaws
>
> Agreed, though I'd modify the definition of that case to be "remain
> frozen until the last thaw occurs". That has the advantage that
> it's relatively simple to implement with just a counter...

I agree this idea.
But I have one concern. When device-mapper's freeze follows FIFREEZE,
can device-mapper freeze only device-mapper's part correctly?
And when device-mapper's thaw follows FITHAW,
can device-mapper thaw only device-mapper's part?

Cheers, Takashi 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/