Messages in this thread | | | Date | Thu, 16 Oct 2008 14:35:59 +0200 | From | Daniel Lezcano <> | Subject | Re: [RFC v6][PATCH 0/9] Kernel based checkpoint/restart |
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Oren Laadan wrote: > Cedric Le Goater wrote: >> Dave Hansen wrote: >>> On Mon, 2008-10-13 at 10:13 +0200, Cedric Le Goater wrote: >>>> hmm, that's rather complex, because we have to take into account the >>>> kernel stack, no ? This is what Andrey was trying to solve in his patchset >>>> back in September : >>>> >>>> http://lkml.org/lkml/2008/9/3/96 >>>> >>>> the restart phase simulates a clone and switch_to to (not) restore the kernel >>>> stack. right ? >>> Do we ever have to worry about the kernel stack if we simply say that >>> tasks have to be *in* userspace when we checkpoint them. >> at a syscall boundary for example. that would make our life easier >> definitely. >> > > The ideal situation is never worry about kernel stack: either we catch > the task in user space or at a syscall boundary. This is taken care of > by freezing the tasks prior to checkpoint. > > The one exception (and it is a tedious one !) are states in which the > task is already frozen by definition: any ptrace blocking point where > the tracee waits for the tracer to grant permission to proceed with > its execution. Another example is in vfork(), waiting for completion.
I would say these are perfect places for "may be non-checkpointable" :)
> In both cases, there will be a kernel stack and we cannot avoid it. > The bad news is that it may be a bit tedious to restart these cases. > The good news, however, is that they are very well defined locations > with well defined semantics. So upon restart all that is needed is > to emulate the expected behavior had we not been checkpointed. This, > luckily, does not require rebuilding the kernel stack, but instead > some smart glue code for a finite set of special cases.
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