net: Detect drivers that reschedule NAPI and exhaust budget

The commit d75b1ade567ffab085e8adbbdacf0092d10cd09c (net: less
interrupt masking in NAPI) required drivers to leave poll_list
empty if the entire budget is consumed.

We have already had two broken drivers so let's add a check for
this.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 493ae8ee569f..c0cf1293df06 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4602,6 +4602,15 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
                 napi_gro_flush(n, HZ >= 1000);
         }
 
+        /* Some drivers may have called napi_schedule
+         * prior to exhausting their budget.
+         */
+        if (unlikely(!list_empty(&n->poll_list))) {
+                pr_warn_once("%s: Budget exhausted after napi rescheduled\n",
+                             n->dev ? n->dev->name : "backlog");
+                goto out_unlock;
+        }
+
         list_add_tail(&n->poll_list, repoll);
 
 out_unlock: