[Xen-devel] [PATCH 2/4] net: Detect drivers that reschedule NAPI and exhaust budget

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxxx>
---

 net/core/dev.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index f7c4f4e..4a9c424 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:

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