05.08.2019 14:32, Max Reitz wrote:
> On 02.08.19 20:58, Vladimir Sementsov-Ogievskiy wrote:
>> hbitmap_reset is broken: it rounds up the requested region. It leads to
>> the following bug, which is shown by fixed test:
>>
>> assume granularity = 2
>> set(0, 3) # count becomes 4
>> reset(0, 1) # count becomes 2
>>
>> But user of the interface assume that virtual bit 1 should be still
>> dirty, so hbitmap should report count to be 4!
>>
>> In other words, because of granularity, when we set one "virtual" bit,
>> yes, we make all "virtual" bits in same chunk to be dirty. But this
>> should not be so for reset.
>>
>> Fix this, aligning bound correctly.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
>> ---
>>
>> Hi all!
>>
>> Hmm, is it a bug or feature? :)
>> I don't have a test for mirror yet, but I think that sync mirror may be
>> broken
>> because of this, as do_sync_target_write() seems to be using unaligned reset.
>>
>> tests/test-hbitmap.c | 2 +-
>> util/hbitmap.c | 24 +++++++++++++++++++-----
>> 2 files changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
>> index 592d8219db..0008025a9f 100644
>> --- a/tests/test-hbitmap.c
>> +++ b/tests/test-hbitmap.c
>> @@ -424,7 +424,7 @@ static void test_hbitmap_granularity(TestHBitmapData
>> *data,
>> hbitmap_test_set(data, 0, 3);
>> g_assert_cmpint(hbitmap_count(data->hb), ==, 4);
>> hbitmap_test_reset(data, 0, 1);
>> - g_assert_cmpint(hbitmap_count(data->hb), ==, 2);
>> + g_assert_cmpint(hbitmap_count(data->hb), ==, 4);
>> }
>>
>> static void test_hbitmap_iter_granularity(TestHBitmapData *data,
>> diff --git a/util/hbitmap.c b/util/hbitmap.c
>> index 7905212a8b..61a813994a 100644
>> --- a/util/hbitmap.c
>> +++ b/util/hbitmap.c
>> @@ -473,15 +473,29 @@ void hbitmap_reset(HBitmap *hb, uint64_t start,
>> uint64_t count)
>> {
>> /* Compute range in the last layer. */
>> uint64_t first;
>> - uint64_t last = start + count - 1;
>> + uint64_t last;
>> + uint64_t end = start + count;
>> + uint64_t gran = UINT64_C(1) << hb->granularity;
>>
>> - trace_hbitmap_reset(hb, start, count,
>> - start >> hb->granularity, last >> hb->granularity);
>> + /*
>> + * We should clear only bits, fully covered by requested region.
>> Otherwise
>> + * we may clear something that is actually still dirty.
>> + */
>> + first = DIV_ROUND_UP(start, gran);
>>
>> - first = start >> hb->granularity;
>> - last >>= hb->granularity;
>> + if (end == hb->orig_size) {
>
> This should be “>=”.
>
> There are callers that don’t make sure that start + count <=
> hb->orig_size (e.g. the backup job just calls it with multiples of
> cluster_size, which may or may not end up at the image end; and
> hbitmap_truncate() just uses “hb->size << hb->granularity” as the end,
> which is arguably not ideal, but that’s how it is).
>
Ah, yes, you are right. Originally, I had and assertion that end <=
hb->orig_size,
but it failed with test because of these cases. I dropped it and forgot to
update
the condition. Ogh, this is how such small huge bugs are appearing..
--
Best regards,
Vladimir
