> -----Original Message-----
> From: Wei Liu [mailto:wei.l...@citrix.com]
> Sent: 21 June 2017 10:21
> To: netdev@vger.kernel.org
> Cc: Xen-devel <xen-de...@lists.xenproject.org>; Paul Durrant
> <paul.durr...@citrix.com>; David Miller <da...@davemloft.net>; jean-
> lo...@dupond.be; Wei Liu <wei.l...@citrix.com>
> Subject: [PATCH net] xen-netback: correctly schedule rate-limited queues
>
> Add a flag to indicate if a queue is rate-limited. Test the flag in
> NAPI poll handler and avoid rescheduling the queue if true, otherwise
> we risk locking up the host. The rescheduling will be done in the
> timer callback function.
>
> Reported-by: Jean-Louis Dupond <jean-lo...@dupond.be>
> Signed-off-by: Wei Liu <wei.l...@citrix.com>
> Tested-by: Jean-Louis Dupond <jean-lo...@dupond.be>
Reviewed-by: Paul Durrant <paul.durr...@citrix.com>
> ---
> drivers/net/xen-netback/common.h | 1 +
> drivers/net/xen-netback/interface.c | 6 +++++-
> drivers/net/xen-netback/netback.c | 6 +++++-
> 3 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-
> netback/common.h
> index 530586be05b4..5b1d2e8402d9 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -199,6 +199,7 @@ struct xenvif_queue { /* Per-queue data for xenvif */
> unsigned long remaining_credit;
> struct timer_list credit_timeout;
> u64 credit_window_start;
> + bool rate_limited;
>
> /* Statistics */
> struct xenvif_stats stats;
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-
> netback/interface.c
> index 8397f6c92451..e322a862ddfe 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -106,7 +106,11 @@ static int xenvif_poll(struct napi_struct *napi, int
> budget)
>
> if (work_done < budget) {
> napi_complete_done(napi, work_done);
> - xenvif_napi_schedule_or_enable_events(queue);
> + /* If the queue is rate-limited, it shall be
> + * rescheduled in the timer callback.
> + */
> + if (likely(!queue->rate_limited))
> + xenvif_napi_schedule_or_enable_events(queue);
> }
>
> return work_done;
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> netback/netback.c
> index 602d408fa25e..5042ff8d449a 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -180,6 +180,7 @@ static void tx_add_credit(struct xenvif_queue
> *queue)
> max_credit = ULONG_MAX; /* wrapped: clamp to
> ULONG_MAX */
>
> queue->remaining_credit = min(max_credit, max_burst);
> + queue->rate_limited = false;
> }
>
> void xenvif_tx_credit_callback(unsigned long data)
> @@ -686,8 +687,10 @@ static bool tx_credit_exceeded(struct xenvif_queue
> *queue, unsigned size)
> msecs_to_jiffies(queue->credit_usec / 1000);
>
> /* Timer could already be pending in rare cases. */
> - if (timer_pending(&queue->credit_timeout))
> + if (timer_pending(&queue->credit_timeout)) {
> + queue->rate_limited = true;
> return true;
> + }
>
> /* Passed the point where we can replenish credit? */
> if (time_after_eq64(now, next_credit)) {
> @@ -702,6 +705,7 @@ static bool tx_credit_exceeded(struct xenvif_queue
> *queue, unsigned size)
> mod_timer(&queue->credit_timeout,
> next_credit);
> queue->credit_window_start = next_credit;
> + queue->rate_limited = true;
>
> return true;
> }
> --
> 2.11.0
