Re: [PATCH 2/3] block: Fix locking in qmp_block_resize()

[Vladimir Sementsov-Ogievskiy]

03.12.2020 20:23, Kevin Wolf wrote:
> The drain functions assume that we hold the AioContext lock of the
> drained block node. Make sure to actually take the lock.
>
> Cc: qemu-stable@nongnu.org
> Fixes: eb94b81a94bce112e6b206df846c1551aaf6cab6
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   blockdev.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index 229d2cce1b..0535a8dc9e 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -2481,13 +2481,16 @@ void coroutine_fn qmp_block_resize(bool has_device, 
> const char *device,
>           return;
>       }
>   
> +    bdrv_co_lock(bs);
>       bdrv_drained_begin(bs);
> +    bdrv_co_unlock(bs);
> +
>       old_ctx = bdrv_co_enter(bs);
>       blk_truncate(blk, size, false, PREALLOC_MODE_OFF, 0, errp);
>       bdrv_co_leave(bs, old_ctx);
> -    bdrv_drained_end(bs);
>   
>       bdrv_co_lock(bs);
> +    bdrv_drained_end(bs);
>       blk_unref(blk);
>       bdrv_co_unlock(bs);
>   }

Can't we just do

    old_ctx = bdrv_co_enter(bs);

    bdrv_drained_begin(bs);
                                                                                
    blk_truncate(blk, size, false, PREALLOC_MODE_OFF, 0, errp);
                                                                                  
    bdrv_drained_end(bs);
    blk_unref(blk);

    bdrv_co_leave(bs, old_ctx);


? This way we have one acquire/release section instead of three in a row.. But 
then we probably need addition bdrv_ref/bdrv_unref, to not crash with final 
bdrv_co_leave after blk_unref.

Also, preexisting, but it seems not good that coroutine_fn qmp_block_resize is 
called from non-coroutine hmp_block_resize()

anyway:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

--
Best regards,
Vladimir