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Re: vvar, gup && coredump
- From: Andy Lutomirski <luto at amacapital dot net>
- To: Pedro Alves <palves at redhat dot com>
- Cc: Oleg Nesterov <oleg at redhat dot com>, Jan Kratochvil <jan dot kratochvil at redhat dot com>, Sergio Durigan Junior <sergiodj at redhat dot com>, GDB Patches <gdb-patches at sourceware dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>
- Date: Thu, 12 Mar 2015 11:25:43 -0700
- Subject: Re: vvar, gup && coredump
- Authentication-results: sourceware.org; auth=none
- References: <878ufc9kau dot fsf at redhat dot com> <20150305154827 dot GA9441 at host1 dot jankratochvil dot net> <87zj7r5fpz dot fsf at redhat dot com> <20150305205744 dot GA13165 at host1 dot jankratochvil dot net> <20150311200052 dot GA22654 at redhat dot com> <20150312143438 dot GA4338 at redhat dot com> <CALCETrW5rmAHutzm_OwK2LTd_J0XByV3pvWGyW=AmC=v7rLfhQ at mail dot gmail dot com> <20150312165423 dot GA10073 at redhat dot com> <20150312174653 dot GA13086 at redhat dot com> <5501D8CF dot 7020204 at redhat dot com>
On Thu, Mar 12, 2015 at 11:19 AM, Pedro Alves <email@example.com> wrote:
> On 03/12/2015 05:46 PM, Oleg Nesterov wrote:
>> On 03/12, Oleg Nesterov wrote:
>>> Yes, this is true. OK, lets not dump it.
>> OTOH. We can probably add ->access() into special_mapping_vmops, this
>> way __access_remote_vm() could work even if gup() fails ?
>> Jan, Sergio. How much do we want do dump this area ? The change above
>> should be justified.
> Memory mappings that weren't touched since they were initially mapped can
> be retrieved from the program binary and the shared libraries, even if
> the core dump is moved to another machine. However, in vvar case,
> sounds like there's nowhere to read it from offline? In that case,
> it could be justified to dump it.
This is why we currently dump the vdso text. On arm64 (the only other
architecture that uses a real vma for vvar data IIRC), we use a more
normal vma and we dump it. x86 is the odd one out here.
We could just leave the kernel alone. The data that gets dumped is of
dubious value, but it could be slightly helpful when debugging vdso
crashes*, but, of course, dumping it is inherently racy.
* The vdso never crashes :)
> Pedro Alves
AMA Capital Management, LLC