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Re: [Qemu-devel] [PATCH] ide: avoid unbounded recursion
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] ide: avoid unbounded recursion |
Date: |
Thu, 12 Jan 2017 14:11:45 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Thu, Jan 12, 2017 at 11:51:32AM +0100, Paolo Bonzini wrote:
> The end_transfer_func can call ide_transfer_start immediately, before
> returning, and unbounded recursion can happen at least for
> ide_atapi_cmd_reply_end. Use a bottom half to defer the call and
> limit stack usage.
>
> Cc: Peter Lieven <address@hidden>
> Cc: John Snow <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
> hw/ide/core.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index 43709e5..7b9831f 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -482,6 +482,13 @@ static void ide_clear_retry(IDEState *s)
> s->bus->retry_nsector = 0;
> }
>
> +static void ide_start_transfer_bh_cb(void *opaque)
> +{
> + IDEDMA *dma = opaque;
> +
> + dma->ops->start_transfer(dma);
> +}
> +
> /* prepare data transfer and tell what to do after */
> void ide_transfer_start(IDEState *s, uint8_t *buf, int size,
> EndTransferFunc *end_transfer_func)
> @@ -494,7 +501,12 @@ void ide_transfer_start(IDEState *s, uint8_t *buf, int
> size,
> s->status |= DRQ_STAT;
> }
> if (s->bus->dma->ops->start_transfer) {
> - s->bus->dma->ops->start_transfer(s->bus->dma);
> + /* There can be unbounded recursion between ops->start_transfer
> + * and end_transfer_func, so defer to a bottom half.
> + */
> + aio_bh_schedule_oneshot(qemu_get_aio_context(),
> + ide_start_transfer_bh_cb,
> + s->bus->dma);
Are you sure this is safe?
I wonder if there are races with device reset, vmsave, or vcpu hw
register accesses.
Stefan
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