linux-kernel - Re: INFO: task hung in sync

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Message-ID: <CACT4Y+b8CzoTXTitPX-O83p5zgEjsR37U3TPyQ0=4fGeNJHdiA@mail.gmail.com>
Date:   Thu, 8 Feb 2018 18:17:48 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Jan Kara <jack@...e.cz>, Andi Kleen <ak@...ux.intel.com>,
        syzbot <syzbot+283c3c447181741aea28@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>, jlayton@...hat.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Ingo Molnar <mingo@...nel.org>, rgoldwyn@...e.com,
        syzkaller-bugs@...glegroups.com, linux-fsdevel@...r.kernel.org
Subject: Re: INFO: task hung in sync_blockdev

On Thu, Feb 8, 2018 at 5:23 PM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>
>
> On 02/08/2018 07:18 PM, Jan Kara wrote:
>
>>> By "full kernel crashdump" you mean kdump thing, or something else?
>>
>> Yes, the kdump thing (for KVM guest you can grab the memory dump also from
>> the host in a simplier way and it should be usable with the crash utility
>> AFAIK).
>>
>
> In QEMU monitor 'dump-guest-memory' command:
>
> (qemu) help dump-guest-memory
> dump-guest-memory [-p] [-d] [-z|-l|-s] filename [begin length] -- dump guest memory into file 'filename'.
>                         -p: do paging to get guest's memory mapping.
>                         -d: return immediately (do not wait for completion).
>                         -z: dump in kdump-compressed format, with zlib compression.
>                         -l: dump in kdump-compressed format, with lzo compression.
>                         -s: dump in kdump-compressed format, with snappy compression.
>                         begin: the starting physical address.
>                         length: the memory size, in bytes


Nice!
Do you know straight away if it's scriptable/automatable? Or do I just
send some magic sequence of bytes representing ^A+C,
dump-guest-memory, \n to stdin pipe?

Unfortunately, syzbot uses GCE VMs for testing, and there does not
seem to be such feature on GCE...