Re: [Qemu-devel] [PATCH] blockdev: fix missed target unref for drive-backup

[John Snow <jsnow@redhat.com>]

On 5/13/19 7:13 AM, Kevin Wolf wrote:
> Am 10.05.2019 um 23:52 hat John Snow geschrieben:
>> If the bitmap can't be used for whatever reason, we skip putting down
>> the reference. Fix that.
>>
>> In practice, this means that if you attempt to gracefully exit QEMU
>> after a backup command being rejected, bdrv_close_all will fail and
>> tell you some unpleasant things via assert().
>>
>> Reported-by: aihua liang <aliang@redhat.com>
>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1703916
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>  blockdev.c | 12 +++++-------
>>  1 file changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 79fbac8450..278ecdd122 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -3525,8 +3525,7 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
>>      if (set_backing_hd) {
>>          bdrv_set_backing_hd(target_bs, source, &local_err);
>>          if (local_err) {
>> -            bdrv_unref(target_bs);
>> -            goto out;
>> +            goto unref;
>>          }
>>      }
>>  
>> @@ -3534,11 +3533,10 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
>>          bmap = bdrv_find_dirty_bitmap(bs, backup->bitmap);
>>          if (!bmap) {
>>              error_setg(errp, "Bitmap '%s' could not be found", backup->bitmap);
>> -            bdrv_unref(target_bs);
>> -            goto out;
>> +            goto unref;
>>          }
>>          if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_DEFAULT, errp)) {
>> -            goto out;
>> +            goto unref;
>>          }
>>      }
>>      if (!backup->auto_finalize) {
>> @@ -3552,12 +3550,12 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
>>                              backup->sync, bmap, backup->compress,
>>                              backup->on_source_error, backup->on_target_error,
>>                              job_flags, NULL, NULL, txn, &local_err);
>> -    bdrv_unref(target_bs);
>>      if (local_err != NULL) {
>>          error_propagate(errp, local_err);
>> -        goto out;
> 
> Please leave a 'goto unref' here so we can later add more code without
> modifying unrelated error paths (or, more likely, forgetting to modify
> them).
> 

Oh, that makes sense.

>>      }
>>  
>> +unref:
>> +    bdrv_unref(target_bs);
>>  out:
>>      aio_context_release(aio_context);
>>      return job;
> 
> With this fixed:
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> 

Thanks!