Re: [Qemu-devel] [PULL 11/13] migration: add postcopy migration of dirty bitmaps

[John Snow]

On 06/20/2018 12:43 PM, Peter Maydell wrote:
> On 27 April 2018 at 14:22, Peter Maydell <address@hidden> wrote:
>> On 13 March 2018 at 21:14, John Snow <address@hidden> wrote:
>>> From: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>
>>> Postcopy migration of dirty bitmaps. Only named dirty bitmaps are migrated.
>>>
>>> If destination qemu is already containing a dirty bitmap with the same name
>>> as a migrated bitmap (for the same node), then, if their granularities are
>>> the same the migration will be done, otherwise the error will be generated.
>>>
>>> If destination qemu doesn't contain such bitmap it will be created.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>> Reviewed-by: Dr. David Alan Gilbert <address@hidden>
>>> Message-id: address@hidden
>>> [Changed '+' to '*' as per list discussion. --js]
>>> Signed-off-by: John Snow <address@hidden>
>>
>>> +static int init_dirty_bitmap_migration(void)
>>> +{
>>
>> Hi; Coverity (CID1390625) complains about a possible dereference
>> after NULL check in this function:
>>
>>> +    BlockDriverState *bs;
>>> +    BdrvDirtyBitmap *bitmap;
>>> +    DirtyBitmapMigBitmapState *dbms;
>>> +    BdrvNextIterator it;
>>> +
>>> +    dirty_bitmap_mig_state.bulk_completed = false;
>>> +    dirty_bitmap_mig_state.prev_bs = NULL;
>>> +    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);
>>> +        }
>>
>> The 'bs' test in this while() loop implies that we might
>> leave the loop because bs == NULL...
>>
>>> +
>>> +        for (bitmap = bdrv_dirty_bitmap_next(bs, NULL); bitmap;
>>
>> ...but this call to bdrv_dirty_bitmap_next() will always
>> dereference bs, so if it's NULL we'll crash.
>>
>>> +             bitmap = bdrv_dirty_bitmap_next(bs, bitmap))
> 
> Hi -- just a nudge that Coverity thinks this one is still unfixed.
> 
> thanks
> -- PMM
> 

Thank you for the reminder, I've been a bit scatter-brained recently.