[Xen-devel] net: Detect drivers that reschedule NAPI and exhaust budget

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

On Sat, Dec 20, 2014 at 11:23:27AM +1100, Herbert Xu wrote:
>
> A similar bug exists in virtio_net.

In order to detect other drivers doing this we should add something
like this.

-- >8 --
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>

diff --git a/net/core/dev.c b/net/core/dev.c
index f411c28..88f9725 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4620,7 +4620,11 @@ static void net_rx_action(struct softirq_action *h)
                                         */
                                        napi_gro_flush(n, HZ >= 1000);
                                }
-                               list_add_tail(&n->poll_list, &repoll);
+                               /* Some drivers may have called napi_schedule
+                                * prior to exhausting their budget.
+                                */
+                               if (!WARN_ON_ONCE(!list_empty(&n->poll_list)))
+                                       list_add_tail(&n->poll_list, &repoll);
                        }
                }
 
Cheers,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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