Re: [Qemu-devel] [PATCH] rbd block driver fix race between aio completition and aio cancel

[Stefan Priebe - Profihost AG]

Hi,

i hope i've done everything correctly. I've send a new v4 patch.

Am 29.11.2012 14:58, schrieb Stefan Hajnoczi:
> On Thu, Nov 22, 2012 at 11:00:19AM +0100, Stefan Priebe wrote:
> > @@ -406,10 +401,11 @@ static void qemu_rbd_complete_aio(RADOSCB *rcb)
> >               acb->ret = r;
> >           }
> >       }
> > +    acb->status = 0;
> > +
>
> I suggest doing this in the BH.  The qemu_aio_wait() loop in
> qemu_rbd_aio_cancel() needs to wait until the BH has executed.  By
> clearing status in the BH we ensure that no matter in which order
> qemu_aio_wait() invokes BHs and callbacks, we'll always wait until the
> BH has completed before ending the while loop in qemu_rbd_aio_cancel().
>
> > @@ -737,7 +741,8 @@ static BlockDriverAIOCB *rbd_start_aio(BlockDriverState *bs,
> >   failed:
> >       g_free(rcb);
> >       s->qemu_aio_count--;
> > -    qemu_aio_release(acb);
> > +    if (!acb->cancelled)
> > +        qemu_aio_release(acb);
> >       return NULL;
> >   }
>
> This scenario is impossible.  We haven't returned the acb back to the
> caller yet so they could not have invoked qemu_aio_cancel().

Greets,
Stefan