Re: [dpdk-dev] [PATCH] virito: fix reuse index in nested loop

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Mon, Jun 13, 2016 at 09:11:57AM +0000, Tan, Jianfeng wrote:
> 
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> > Sent: Monday, June 13, 2016 4:58 PM
> > To: Tan, Jianfeng
> > Cc: dev@dpdk.org; Xie, Huawei
> > Subject: Re: [PATCH] virito: fix reuse index in nested loop
> > 
> > On Sun, Jun 12, 2016 at 10:05:45AM +0000, Jianfeng Tan wrote:
> > > This patches fixes problem of reusing index of outmost loop in nested
> > > loops. This bug will lead to failure when starting a multi queue
> > > virtio device: rx queues (except from the first one) cannot be started,
> > > expecially their vq_ring cannot be initialized, so that when invoking
> > > rx func on these queues, segment fault happens.
> > >
> > > Fixes: a900472aedef ("virtio: split virtio Rx/Tx queue")
> > 
> > Good catch!
> > 
> > > Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> > > ---
> > >  drivers/net/virtio/virtio_rxtx.c | 36 ++++++++++++++++++++----------------
> > >  1 file changed, 20 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> > > index 2e7205b..b96d0cb 100644
> > > --- a/drivers/net/virtio/virtio_rxtx.c
> > > +++ b/drivers/net/virtio/virtio_rxtx.c
> > > @@ -331,7 +331,7 @@ virtio_dev_rxtx_start(struct rte_eth_dev *dev)
> > >  	 * -	Allocate blank mbufs for the each rx descriptor
> > >  	 *
> > >  	 */
> > > -	int i;
> > > +	int i, j;
> > 
> > However, I don't quite like using "i, j, k" stuff. So, how about
> > renaming "j" to "ring_idx"?
> > 
> > >  	PMD_INIT_FUNC_TRACE();
> > >
> > > @@ -352,15 +352,18 @@ virtio_dev_rxtx_start(struct rte_eth_dev *dev)
> > >  		error = ENOSPC;
> > >
> > >  #ifdef RTE_MACHINE_CPUFLAG_SSSE3
> > > -		if (use_simple_rxtx)
> > > -			for (i = 0; i < vq->vq_nentries; i++) {
> > > -				vq->vq_ring.avail->ring[i] = i;
> > > -				vq->vq_ring.desc[i].flags =
> > VRING_DESC_F_WRITE;
> > > +		if (use_simple_rxtx) {
> > > +			uint16_t k;
> > 
> > We could reuse "ring_idx" here; no need to define yet another iterate var
> > for that.
> 
> Make sense. Besides, since comparison between unsigned and signed is a violation to static code analyzer, I'll redefine these variables as unsigned.
> Such as,
> int i -> uint16_t q_idx
> int j -> uint16_t r_idx
> k -> r_idx

It's nothing big deal, but if I were you, I would keep the var name "i"
unchanged (yes, we need define it to uint16_t), and introduce "ring_idx"
but not "r_idx": I will not sacrifice the readability by saving few
typings.

	--yliu