[dpdk-dev] [PATCH] net/mlx5: handle expected errno properly

Yongseok Koh yskoh at mellanox.com
Tue Aug 28 22:42:18 CEST 2018


On Fri, Aug 24, 2018 at 02:45:00PM +0800, Jack MIN wrote:
> On Thu, Aug 23, 2018 at 02:08:09PM -0700, Yongseok Koh wrote:
> > On Thu, Aug 23, 2018 at 02:38:51PM +0800, Xiaoyu Min wrote:
> > > rte_errno is a per thread variable and is widely used as an
> > > error indicator, which means a function could affect
> > > other functions' results by setting rte_errno carelessly
> > > 
> > > During rxq setup, an EINVAL rte_errno is expected since
> > > the queues are not created yet
> > > So rte_errno is cleared when it is EINVAL as expected
> > > 
> > > Signed-off-by: Xiaoyu Min <jackmin at mellanox.com>
> > > ---
> > >  drivers/net/mlx5/mlx5_rxq.c | 20 +++++++++++++++-----
> > >  1 file changed, 15 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
> > > index 1f7bfd4..e7056e8 100644
> > > --- a/drivers/net/mlx5/mlx5_rxq.c
> > > +++ b/drivers/net/mlx5/mlx5_rxq.c
> > > @@ -443,6 +443,7 @@
> > >  	struct mlx5_rxq_data *rxq = (*priv->rxqs)[idx];
> > >  	struct mlx5_rxq_ctrl *rxq_ctrl =
> > >  		container_of(rxq, struct mlx5_rxq_ctrl, rxq);
> > > +	int ret = 0;
> > >  
> > >  	if (!rte_is_power_of_2(desc)) {
> > >  		desc = 1 << log2above(desc);
> > > @@ -459,13 +460,21 @@
> > >  		rte_errno = EOVERFLOW;
> > >  		return -rte_errno;
> > >  	}
> > > -	if (!mlx5_rxq_releasable(dev, idx)) {
> > > +	ret = mlx5_rxq_releasable(dev, idx);
> > > +	if (!ret) {
> > >  		DRV_LOG(ERR, "port %u unable to release queue index %u",
> > >  			dev->data->port_id, idx);
> > >  		rte_errno = EBUSY;
> > >  		return -rte_errno;
> > > +	} else if (ret == -EINVAL) {
> > > +		/**
> > > +		 * on the first time, rx queue doesn't exist,
> > > +		 * so just ignore this error and reset rte_errno.
> > > +		 */
> > > +		rte_errno = 0;
> > 
> > Unless this function returns failure, the rte_errno will be ignored by caller
> > and caller shouldn't assume rte_errno has 0. Caller will assume it is garbage
> > data in case of success. So we can silently ignore this case. Does it cause any
> > issue in application side?
> > 
> Not application side but mlx5 PMD this time:
> **mlx5_fdir_filter_delete** 
> which just _return -rte_errno;_

Looks like an error. mlx5_fdir_filter_delete() can't be like that. We seem to
have lost the code while refactoring it. Let take it offline.

> For sure, _mlx5_fdir_filter_delete_ should be more defensive, should not assume
> rte_errno is zero if no error happened.
> However if the caller know that an error will happen and rte_errno will become
> meaningless (garbage) for the succeeding functions, Catching the expected error
> and resetting rte_errno will be better. What do you think?

Still don't understand clearly. There would be many other similar cases where we
don't clear rte_errno when returning success. I don't understand why this case
should be taken as a special one??

Thanks
Yongseok


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