From: David Vrabel Date: Tue, 16 Dec 2014 18:59:46 +0000 (+0000) Subject: xen-netfront: use napi_complete() correctly to prevent Rx stalling X-Git-Tag: v3.19-rc1~32^2~14 X-Git-Url: http://git.cascardo.info/?p=cascardo%2Flinux.git;a=commitdiff_plain;h=6a6dc08ff6395f58be3ee568cb970ea956f16819 xen-netfront: use napi_complete() correctly to prevent Rx stalling After d75b1ade567ffab085e8adbbdacf0092d10cd09c (net: less interrupt masking in NAPI) the napi instance is removed from the per-cpu list prior to calling the n->poll(), and is only requeued if all of the budget was used. This inadvertently broke netfront because netfront does not use NAPI correctly. If netfront had not used all of its budget it would do a final check for any Rx responses and avoid calling napi_complete() if there were more responses. It would still return under budget so it would never be rescheduled. The final check would also not re-enable the Rx interrupt. Additionally, xenvif_poll() would also call napi_complete() /after/ enabling the interrupt. This resulted in a race between the napi_complete() and the napi_schedule() in the interrupt handler. The use of local_irq_save/restore() avoided by race iff the handler is running on the same CPU but not if it was running on a different CPU. Fix both of these by always calling napi_compete() if the budget was not all used, and then calling napi_schedule() if the final checks says there's more work. Signed-off-by: David Vrabel Cc: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index 2f0a9ce9ff73..22bcb4e12e2a 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -977,7 +977,6 @@ static int xennet_poll(struct napi_struct *napi, int budget) struct sk_buff_head rxq; struct sk_buff_head errq; struct sk_buff_head tmpq; - unsigned long flags; int err; spin_lock(&queue->rx_lock); @@ -1050,15 +1049,11 @@ err: if (work_done < budget) { int more_to_do = 0; - napi_gro_flush(napi, false); - - local_irq_save(flags); + napi_complete(napi); RING_FINAL_CHECK_FOR_RESPONSES(&queue->rx, more_to_do); - if (!more_to_do) - __napi_complete(napi); - - local_irq_restore(flags); + if (more_to_do) + napi_schedule(napi); } spin_unlock(&queue->rx_lock);