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Re: [Xen-devel] [xen-unstable test] 123379: regressions - FAIL

  • To: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Fri, 8 Jun 2018 12:12:46 +0200
  • Autocrypt: addr=jgross@xxxxxxxx; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>
  • Delivery-date: Fri, 08 Jun 2018 10:12:55 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 07/06/18 13:30, Juergen Gross wrote:
> On 06/06/18 11:40, Juergen Gross wrote:
>> On 06/06/18 11:35, Jan Beulich wrote:
>>>>>> On 05.06.18 at 18:19, <ian.jackson@xxxxxxxxxx> wrote:
>>>>>>  test-amd64-i386-libvirt-qemuu-debianhvm-amd64-xsm 14 
>>>>>> guest-saverestore.2 
>>>> I thought I would reply again with the key point from my earlier mail
>>>> highlighted, and go a bit further.  The first thing to go wrong in
>>>> this was:
>>>> 2018-05-30 22:12:49.320+0000: xc: Failed to get types for pfn batch (14 = 
>>>> Bad address): Internal error
>>>> 2018-05-30 22:12:49.483+0000: xc: Save failed (14 = Bad address): Internal 
>>>> error
>>>> 2018-05-30 22:12:49.648+0000: libxl-save-helper: complete r=-1: Bad address
>>>> You can see similar messages in the other logfile:
>>>> 2018-05-30 22:12:49.650+0000: libxl: 
>>>> libxl_stream_write.c:350:libxl__xc_domain_save_done: Domain 3:saving 
>>>> domain: domain responded to suspend request: Bad address
>>>> All of these are reports of the same thing: xc_get_pfn_type_batch at
>>>> xc_sr_save.c:133 failed with EFAULT.  I'm afraid I don't know why.
>>>> There is no corresponding message in the host's serial log nor the
>>>> dom0 kernel log.
>>> I vaguely recall from the time when I had looked at the similar Windows
>>> migration issues that the guest is already in the process of being cleaned
>>> up when these occur. Commit 2dbe9c3cd2 ("x86/mm: silence a pointless
>>> warning") intentionally suppressed a log message here, and the
>>> immediately following debugging code (933f966bcd x86/mm: add
>>> temporary debugging code to get_page_from_gfn_p2m()) was reverted
>>> a little over a month later. This wasn't as a follow-up to another patch
>>> (fix), but following the discussion rooted at
>>> https://lists.xenproject.org/archives/html/xen-devel/2017-06/msg00324.html
>> That was -ESRCH, not -EFAULT.
> I've looked a little bit more into this.
> As we are seeing EFAULT being returned by the hypervisor this either
> means the tools are specifying an invalid address (quite unlikely)
> or the buffers are not as MAP_LOCKED as we wish them to be.
> Is there a way to see whether the host was experiencing some memory
> shortage, so the buffers might have been swapped out?
> man mmap tells me: "This implementation will try to populate (prefault)
> the whole range but the mmap call doesn't fail with ENOMEM if this
> fails. Therefore major faults might happen later on."
> And: "One should use mmap(2) plus mlock(2) when major faults are not
> acceptable after the initialization of the mapping."
> With osdep_alloc_pages() in tools/libs/call/linux.c touching all the
> hypercall buffer pages before doing the hypercall I'm not sure this
> could be an issue.
> Any thoughts on that?

Ian, is there a chance to dedicate a machine to a specific test trying
to reproduce the problem? In case we manage to get this failure in a
reasonable time frame I guess the most promising approach would be to
use a test hypervisor producing more debug data. If you think this is
worth doing I can write a patch.


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