Re: [Qemu-devel] [PATCH] [qemu-devel] fix wrong order when doing live block migration setup

[Chai Wen]

Hi,

Sorry for forgetting to cc maintainers.
I got this issue when doing live migration test, and simple steps to reproduce 
are
    master: qemu -enable-kvm -smp 1 -m 512 -drive file=/data1/src.img,if=virtio 
\
                 -net none -monitor stdio -vnc 0:2
    slave:  qemu -enable-kvm -smp 1 -m 512 -dirve 
file=/data2/dest.img,if=virtio \
                 -net none -monitor stdio -vnc 0:3 -incoming tcp:127.0.0.1:3333 
\

when doing migration cmd "migrate -b tcp:127.0.0.1:3333" in master's monitor,
it throws out a segfault error.

After checking some code of block migration, I think there is something wrong 
with the
setup sequence in block migration setup.

thanks
chai wen


On 05/27/2014 04:54 PM, chai wen wrote:

> If we want to track dirty blocks using dirty_maps on a BlockDriverState
> when doing live block-migration, its correspoding 'BlkMigDevState' should be
> add to block_mig_state.bmds_list firstly for subsequent processing.
> Otherwise set_dirty_tracking will do nothing on an empty list than allocating
> dirty_bitmaps for them.
> 
> And what's the worse, bdrv_get_dirty_count will access the
> bmds->dirty_maps directly, there could be a segfault as the reasons
> above.
> 
> Signed-off-by: chai wen <address@hidden>
> ---
>  block-migration.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/block-migration.c b/block-migration.c
> index 56951e0..43203aa 100644
> --- a/block-migration.c
> +++ b/block-migration.c
> @@ -626,6 +626,7 @@ static int block_save_setup(QEMUFile *f, void *opaque)
>              block_mig_state.submitted, block_mig_state.transferred);
>  
>      qemu_mutex_lock_iothread();
> +    init_blk_migration(f);
>  
>      /* start track dirty blocks */
>      ret = set_dirty_tracking();
> @@ -635,7 +636,6 @@ static int block_save_setup(QEMUFile *f, void *opaque)
>          return ret;
>      }
>  
> -    init_blk_migration(f);
>  
>      qemu_mutex_unlock_iothread();
>  



-- 
Regards

Chai Wen