Re: [Qemu-devel] [PATCH for-2.11] qcow2: Fix overly broad madvise()

[Max Reitz <mreitz@redhat.com>]

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On 2017-11-15 10:09, Alberto Garcia wrote:
> On Tue 14 Nov 2017 07:41:27 PM CET, Max Reitz wrote:
>> @mem_size and @offset are both size_t, thus subtracting them from one
>> another will just return a big size_t if mem_size < offset -- even more
>> obvious here because the result is stored in another size_t.
>>
>> Checking that result to be positive is therefore not sufficient to
>> excluse the case that offset > mem_size.  Thus, we currently sometimes
>> issue an madvise() over a very large address range.
>>
>> This is triggered by iotest 163, but with -m64, this does not result in
>> tangible problems.  But with -m32, this test produces three segfaults,
>> all of which are fixed by this patch.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
> 
> Oh, I guess this happens when the page size is larger than the cluster
> size? Otherwise I don't see how...
> 
> Reviewed-by: Alberto Garcia <berto@igalia.com>

Yes, the test uses 512 byte clusters.

Max


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