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Re: [Qemu-devel] [PATCHv4] rbd block driver fix race between aio complet
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCHv4] rbd block driver fix race between aio completition and aio cancel |
Date: |
Thu, 29 Nov 2012 10:23:29 -0500 (EST) |
----- Messaggio originale -----
> Da: "Stefan Priebe" <address@hidden>
> A: address@hidden
> Cc: address@hidden, "josh durgin" <address@hidden>, address@hidden,
> address@hidden,
> "Stefan Priebe" <address@hidden>
> Inviato: Giovedì, 29 novembre 2012 15:28:35
> Oggetto: [PATCHv4] rbd block driver fix race between aio completition and aio
> cancel
>
> This one fixes a race which qemu had also in iscsi block driver
> between cancellation and io completition.
>
> qemu_rbd_aio_cancel was not synchronously waiting for the end of
> the command.
>
> To archieve this it introduces a new status flag which uses
> -EINPROGRESS.
>
> Changes since PATCHv3:
> - removed unnecessary if condition in rbd_start_aio as we
> haven't start io yet
> - moved acb->status = 0 to rbd_aio_bh_cb so qemu_aio_wait always
> waits until BH was executed
>
> Changes since PATCHv2:
> - fixed missing braces
> - added vfree for bounce
>
> Signed-off-by: Stefan Priebe <address@hidden>
> ---
> block/rbd.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index f3becc7..28e94ab 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -77,6 +77,7 @@ typedef struct RBDAIOCB {
> int error;
> struct BDRVRBDState *s;
> int cancelled;
> + int status;
> } RBDAIOCB;
>
> typedef struct RADOSCB {
> @@ -376,12 +377,6 @@ static void qemu_rbd_complete_aio(RADOSCB *rcb)
> RBDAIOCB *acb = rcb->acb;
> int64_t r;
>
> - if (acb->cancelled) {
> - qemu_vfree(acb->bounce);
> - qemu_aio_release(acb);
> - goto done;
> - }
> -
> r = rcb->ret;
>
> if (acb->cmd == RBD_AIO_WRITE ||
> @@ -409,7 +404,6 @@ static void qemu_rbd_complete_aio(RADOSCB *rcb)
> /* Note that acb->bh can be NULL in case where the aio was
> cancelled */
> acb->bh = qemu_bh_new(rbd_aio_bh_cb, acb);
> qemu_bh_schedule(acb->bh);
> -done:
> g_free(rcb);
> }
>
> @@ -568,6 +562,12 @@ static void qemu_rbd_aio_cancel(BlockDriverAIOCB
> *blockacb)
> {
> RBDAIOCB *acb = (RBDAIOCB *) blockacb;
> acb->cancelled = 1;
> +
> + while (acb->status == -EINPROGRESS) {
> + qemu_aio_wait();
> + }
> +
> + qemu_vfree(acb->bounce);
This vfree is not needed, since the BH will run and do the free.
Otherwise looks ok.
> }
>
> static const AIOCBInfo rbd_aiocb_info = {
> @@ -639,6 +639,7 @@ static void rbd_aio_bh_cb(void *opaque)
> acb->common.cb(acb->common.opaque, (acb->ret > 0 ? 0 :
> acb->ret));
> qemu_bh_delete(acb->bh);
> acb->bh = NULL;
> + acb->status = 0;
>
> qemu_aio_release(acb);
> }
> @@ -685,6 +686,7 @@ static BlockDriverAIOCB
> *rbd_start_aio(BlockDriverState *bs,
> acb->s = s;
> acb->cancelled = 0;
> acb->bh = NULL;
> + acb->status = -EINPROGRESS;
>
> if (cmd == RBD_AIO_WRITE) {
> qemu_iovec_to_buf(acb->qiov, 0, acb->bounce, qiov->size);
> --
> 1.7.10.4
>
>