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Re: [PATCH 2/2] tools/migration: Fix potential overflow in send_checkpoint_dirty_pfn_list()

  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 6 Jul 2021 15:56:14 +0200
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Olaf Hering <olaf@xxxxxxxxx>
  • Delivery-date: Tue, 06 Jul 2021 13:56:34 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 06.07.2021 15:19, Andrew Cooper wrote:
> On 06/07/2021 13:58, Olaf Hering wrote:
>> Am Tue, 6 Jul 2021 12:23:32 +0100
>> schrieb Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:
>>> +    count = stats.dirty_count;
>> Is this accurate?
> The live loop relies on it, and it worked correctly the last time I
> tested it.

When still merely investigating in preparation of my recent series,
i.e. without having made changes yet except to add some logging, I
did observe "Bitmap contained more entries than expected..." a
couple of times, with "written" and "entries" typically apart by
just 1 (as determined by extra logging; to be honest I don't recall
if they were farther apart at any point). So the number is _not_
accurate in any event, and cannot be used for other than reporting
purposes (as also expressed elsewhere on this thread).

This also underlines that, unlike you did say in a reply to one of
my patches, this is only a "detail" message, not an error, because
migration happily went on and succeeded.




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