On Mon, Sep 21, 2020 at 4:08 AM Yunsheng Lin <[email protected]> wrote: > > When napi_consume_skb() is called in the tx desc cleaning process, > it is usually in the softirq context(BH disabled, or are processing > softirqs), but it may also be in the task context, such as in the > netpoll or loopback selftest process. > > Currently napi_consume_skb() uses non-zero budget to indicate the > NAPI context, the driver writer may provide the wrong budget when > tx desc cleaning function is reused for both NAPI and non-NAPI > context, see [1]. > > So this patch uses in_softirq() to indicate the NAPI context, which > doesn't necessarily mean in NAPI context, but it shouldn't care if > NAPI context or not as long as it runs in softirq context or with BH > disabled, then _kfree_skb_defer() will push the skb to the particular > cpu' napi_alloc_cache atomically. > > [1] https://lkml.org/lkml/2020/9/15/38 > > Signed-off-by: Yunsheng Lin <[email protected]> > --- > note that budget parameter is not removed in this patch because it > involves many driver changes, we can remove it in separate patch if > this patch is accepted. > --- > net/core/skbuff.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index e077447..03d0d28 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -895,8 +895,10 @@ void __kfree_skb_defer(struct sk_buff *skb) > > void napi_consume_skb(struct sk_buff *skb, int budget) > { > - /* Zero budget indicate non-NAPI context called us, like netpoll */ > - if (unlikely(!budget)) { > + /* called by non-softirq context, which usually means non-NAPI > + * context, like netpoll. > + */ > + if (unlikely(!in_softirq())) { > dev_consume_skb_any(skb); > return; > } > --
I do not think we should add this kind of fuzzy logic, just because _one_ driver author made a mistake. Add a disable_bh() in the driver slow path, and accept the _existing_ semantic, the one that was understood by dozens.
