On 2020/9/21 15:19, Eric Dumazet wrote: > On Mon, Sep 21, 2020 at 4:08 AM Yunsheng Lin <linyunsh...@huawei.com> 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 <linyunsh...@huawei.com> >> --- >> 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.
As my understanding, this patch did not change _existing_ semantic, it still only call _kfree_skb_defer() in softirq context. This patch just remove the requirement that a softirq context hint need to be provided to decide whether calling _kfree_skb_defer(). Yes, we can add DEBUG_NET() clauses to catch this kind of error as you suggested. But why we need such a debug clauses, when we can decide if delaying skb freeing is possible in napi_consume_skb(), why not just use in_softirq() to make this API more easy to use? Just as __dev_kfree_skb_any() API use "in_irq() || irqs_disabled()" checking to handle the irq context and non-irq context. > . >
