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Re: [Qemu-devel] [PATCH] rbd block driver fix race between aio completit
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] rbd block driver fix race between aio completition and aio cancel |
Date: |
Thu, 29 Nov 2012 14:58:51 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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().
Stefan