Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 18 Mar 2015 15:03:27 -0700 | Subject | Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals delivered to 64-bit programs |
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On Wed, Mar 18, 2015 at 2:34 PM, Pavel Emelyanov <xemul@parallels.com> wrote: > On 03/19/2015 12:26 AM, Andy Lutomirski wrote: >> On Wed, Mar 18, 2015 at 1:02 PM, Oleg Nesterov <oleg@redhat.com> wrote: >>> On 03/18, Andrey Wagin wrote: >>>> >>>> This patch fixes the problem. Oleg, could you send this path in the >>>> criu maillist? >>> >>> Sure, will do. >> >> We still haven't answered one question: what's the kernel's position >> on ABI stability wrt CRIU? We clearly shouldn't make changes that >> break the principle of CRIU, but CRIU encodes so many tricky >> assumptions about the inner workings of the kernel that it's really >> tough to avoid breaking old CRIU versions. > > Well, we try hard to use only documented kernel API-s. Isn't the sigframe > considered to be some sort of "stable API"? I mean -- it's visible by the > userspace, nobody prevents glibc or gdb from messing with this stuff just > by reading it from memory. > > If it's "parse-able" e.g. like VDSO is, but we don't do it in CRIU -- then > it's definitely a CRIU BUG to be fixed.
It's certainly parseable by things like gdb. But it's also supposed to be extensible. hpa, any thoughts here?
> >> So... do we introduce somewhat nasty code into the kernel to keep old >> CRIU versions working, or do we require that users who want to restore >> onto new kernels use new CRIU? > > It's OK (I think) to require newer versions of CRIU, it's easy to update > one unlike the kernel ;) > > But if "old" version of CRIU just crash the restored processes on "new" > kernels and there's no way to detect this properly -- that's the problem.
Yeah, that's unfortunate.
I don't have a great idea for how to work around this, unfortunately. Ideally we'd increment some kind of version counter or use an extension mechanism rather than shoving ss into a field that used to be padding.
--Andy
> >> (It seems clear to me that CRIU should apply the patch regardless of >> what the kernel does. It will enable CRIU to work on the same class >> of programs that are fixed by the kernel change that started this >> thread.) >> >> --Andy >> . >> > > Thanks, > Pavel >
-- Andy Lutomirski AMA Capital Management, LLC
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