Re: [dpdk-dev] [PATCH] net/vdev_netvsc: Prevent alarm lost on failed device probe

[Matan Azrad <matan@nvidia.com>]

From: Long Li
> If a device probe fails, the alarm is canceled and will no longer work for
> previously probed devices.
> 
> Fix this by introducing a flag to track if alarm has been set. Because it's
> possible that an alarm is triggered while probing is in progress that may
> modify vdev_netvsc_ctx_list, introduce a lock to protect it.
> 
> Cc: stable@dpdk.org
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
>  drivers/net/vdev_netvsc/vdev_netvsc.c | 41
> +++++++++++++++++++++++++----------
>  1 file changed, 30 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/vdev_netvsc/vdev_netvsc.c
> b/drivers/net/vdev_netvsc/vdev_netvsc.c
> index be8f19c..bd7e308 100644
> --- a/drivers/net/vdev_netvsc/vdev_netvsc.c
> +++ b/drivers/net/vdev_netvsc/vdev_netvsc.c
> @@ -76,6 +76,11 @@ struct vdev_netvsc_ctx {
>  /** Context list is common to all driver instances. */  static LIST_HEAD(,
> vdev_netvsc_ctx) vdev_netvsc_ctx_list =
>         LIST_HEAD_INITIALIZER(vdev_netvsc_ctx_list);
> +/* Lock to protect concurrent accesses to vdev_netvsc_ctx_list */
> +static rte_rwlock_t vdev_netvsc_ctx_list_lock;
> +
> +/* Flag to track if alarm has been set */ static int
> +vdev_netvsc_alarm_set;
> 
>  /** Number of entries in context list. */  static unsigned int
> vdev_netvsc_ctx_count; @@ -454,19 +459,26 @@ static LIST_HEAD(,
> vdev_netvsc_ctx) vdev_netvsc_ctx_list =
>         struct vdev_netvsc_ctx *ctx;
>         int ret;
> 
> +       rte_rwlock_write_lock(&vdev_netvsc_ctx_list_lock);
>         LIST_FOREACH(ctx, &vdev_netvsc_ctx_list, entry) {
>                 ret = vdev_netvsc_foreach_iface(vdev_netvsc_device_probe, 0,
>                       ctx);
>                 if (ret < 0)
>                         break;
>         }
> -       if (!vdev_netvsc_ctx_count)
> +       rte_rwlock_write_unlock(&vdev_netvsc_ctx_list_lock);
> +
> +       if (!vdev_netvsc_ctx_count) {
> +               vdev_netvsc_alarm_set = 0;
>                 return;
> +       }
> +
>         ret = rte_eal_alarm_set(VDEV_NETVSC_PROBE_MS * 1000,
>                                 vdev_netvsc_alarm, NULL);
>         if (ret < 0) {
>                 DRV_LOG(ERR, "unable to reschedule alarm callback: %s",
>                         rte_strerror(-ret));
> +               vdev_netvsc_alarm_set = 0;
>         }
>  }
> 
> @@ -698,34 +710,41 @@ static LIST_HEAD(, vdev_netvsc_ctx)
> vdev_netvsc_ctx_list =
>                         " device.");
>                 goto error;
>         }
> -       rte_eal_alarm_cancel(vdev_netvsc_alarm, NULL);
> +
> +       rte_rwlock_write_lock(&vdev_netvsc_ctx_list_lock);
>         /* Gather interfaces. */
>         ret = vdev_netvsc_foreach_iface(vdev_netvsc_netvsc_probe, 1, name,
>                                         kvargs, specified, &matched);
>         if (ret < 0)
> -               goto error;
> +               goto error_unlock;
>         if (specified && matched < specified) {
>                 if (!force) {
>                         DRV_LOG(ERR, "Cannot find the specified netvsc device");
> -                       goto error;
> +                       goto error_unlock;
>                 }
>                 /* Try to force probing on non-netvsc specified device. */
>                 if (vdev_netvsc_foreach_iface(vdev_netvsc_netvsc_probe, 0, name,
>                                               kvargs, specified, &matched) < 0)
> -                       goto error;
> +                       goto error_unlock;
>                 if (matched < specified) {
>                         DRV_LOG(ERR, "Cannot find the specified device");
> -                       goto error;
> +                       goto error_unlock;
>                 }
>                 DRV_LOG(WARNING, "non-netvsc device was probed as netvsc");
>         }
> -       ret = rte_eal_alarm_set(VDEV_NETVSC_PROBE_MS * 1000,
> +       if (!vdev_netvsc_alarm_set) {
> +               ret = rte_eal_alarm_set(VDEV_NETVSC_PROBE_MS * 1000,
>                                 vdev_netvsc_alarm, NULL);
> -       if (ret < 0) {
> -               DRV_LOG(ERR, "unable to schedule alarm callback: %s",
> -                       rte_strerror(-ret));
> -               goto error;
> +               if (ret < 0)
> +                       DRV_LOG(ERR, "unable to schedule alarm callback: %s",
> +                               rte_strerror(-ret));
> +               else
> +                       vdev_netvsc_alarm_set = 1;
>         }
> +
> +error_unlock:
> +       rte_rwlock_write_unlock(&vdev_netvsc_ctx_list_lock);
> +
>  error:
>         if (kvargs)
>                 rte_kvargs_free(kvargs);
> --

Hi

Nice direction.

As I understand from your patch it looks like you want to add support for the vdev_netvsc driver itself to be hot-plug aware - so it can be probed\removed in run-time (even after EAL initialization).
So I think the title and commit log should be converted to this: net/vdev_netvsc: support driver instance hot-plug
...

More things:
Look on convention of the file - blank line only after variables declarations inside the blocks.

Need to adjust also vdev_netvsc_vdev_remove to the feature. 

Matan