Re: [PATCH v2] migration/dirty-bitmaps: change bitmap enumeration method

[John Snow <jsnow@redhat.com>]

On 12/6/19 5:31 PM, Vladimir Sementsov-Ogievskiy wrote:
> 14.05.2019 23:19, John Snow wrote:
>> Shift from looking at every root BDS to *every* BDS. This will migrate
>> bitmaps that are attached to blockdev created nodes instead of just ones
>> attached to emulated storage devices.
>>
>> Note that this will not migrate anonymous or internal-use bitmaps, as
>> those are defined as having no name.
>>
>> This will also fix the Coverity issues Peter Maydell has been asking
>> about for the past several releases, as well as fixing a real bug.
>>
>> Reported-by: Peter Maydell <peter.maydell@linaro.org>
>> Reported-by: Coverity 😅
> 
> What was the coverity number (I don't believe that it was smile:)?
> 

    Reported-by: Peter Maydell <peter.maydell@linaro.org>
    Reported-by: Coverity 😅
    Reported-by: aihua liang <aliang@redhat.com>
    Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
    Signed-off-by: John Snow <jsnow@redhat.com>
    Message-id: 20190514201926.10407-1-jsnow@redhat.com
    Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1652490
    Fixes: Coverity CID 1390625
    CC: Stefan Hajnoczi <stefanha@redhat.com>
    Signed-off-by: John Snow <jsnow@redhat.com>


> Do someone know, that this patch fixes very-very-very terrible bug?
> 
> Before this patch, here were bdrv_next-based loop, with exists from it,
> but not using bdrv_next_cleanup(). This leads to leaked (incremented) refcnt of
> bds on any failure during this loop!
> 
> Now we faced this bug, in Rhel-based Qemu, so I strongly recommend to fix it in Rhel.

OK, this was fixed for 4.1, and was introduced in b35ebdf076d for
2.12.0, so all versions between have the problem.

> 
>> Reported-by: aihua liang <aliang@redhat.com>
>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1652490
>> Fixes: Coverity CID 1390625
>> CC: Stefan Hajnoczi <stefanha@redhat.com>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   migration/block-dirty-bitmap.c | 14 ++++----------
>>   1 file changed, 4 insertions(+), 10 deletions(-)
>>
>> diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
>> index d1bb863cb6..4a896a09eb 100644
>> --- a/migration/block-dirty-bitmap.c
>> +++ b/migration/block-dirty-bitmap.c
>> @@ -273,7 +273,6 @@ static int init_dirty_bitmap_migration(void)
>>       BlockDriverState *bs;
>>       BdrvDirtyBitmap *bitmap;
>>       DirtyBitmapMigBitmapState *dbms;
>> -    BdrvNextIterator it;
>>       Error *local_err = NULL;
>>   
>>       dirty_bitmap_mig_state.bulk_completed = false;
>> @@ -281,13 +280,8 @@ static int init_dirty_bitmap_migration(void)
>>       dirty_bitmap_mig_state.prev_bitmap = NULL;
>>       dirty_bitmap_mig_state.no_bitmaps = false;
>>   
>> -    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
>> -        const char *drive_name = bdrv_get_device_or_node_name(bs);
>> -
>> -        /* skip automatically inserted nodes */
>> -        while (bs && bs->drv && bs->implicit) {
>> -            bs = backing_bs(bs);
>> -        }
>> +    for (bs = bdrv_next_all_states(NULL); bs; bs = bdrv_next_all_states(bs)) {
>> +        const char *name = bdrv_get_device_or_node_name(bs);
>>   
>>           for (bitmap = bdrv_dirty_bitmap_next(bs, NULL); bitmap;
>>                bitmap = bdrv_dirty_bitmap_next(bs, bitmap))
>> @@ -296,7 +290,7 @@ static int init_dirty_bitmap_migration(void)
>>                   continue;
>>               }
>>   
>> -            if (drive_name == NULL) {
>> +            if (!name || strcmp(name, "") == 0) {
>>                   error_report("Found bitmap '%s' in unnamed node %p. It can't "
>>                                "be migrated", bdrv_dirty_bitmap_name(bitmap), bs);
>>                   goto fail;
>> @@ -313,7 +307,7 @@ static int init_dirty_bitmap_migration(void)
>>   
>>               dbms = g_new0(DirtyBitmapMigBitmapState, 1);
>>               dbms->bs = bs;
>> -            dbms->node_name = drive_name;
>> +            dbms->node_name = name;
>>               dbms->bitmap = bitmap;
>>               dbms->total_sectors = bdrv_nb_sectors(bs);
>>               dbms->sectors_per_chunk = CHUNK_SIZE * 8 *
>>
> 
>