Messages in this thread | | | From | "Takashi Sato" <> | Subject | Re: [dm-devel] Re: [PATCH 3/3] Add timeout feature | Date | Fri, 4 Jul 2008 21:08:09 +0900 |
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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
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