On 2020/11/1 6:38, Jakub Kicinski wrote:
> On Thu, 29 Oct 2020 19:34:48 +0800 Yunsheng Lin wrote:
>> The current semantic for napi_consume_skb() is that caller need
>> to provide non-zero budget when calling from NAPI context, and
>> breaking this semantic will cause hard to debug problem, because
>> _kfree_skb_defer() need to run in atomic context in order to push
>> the skb to the particular cpu' napi_alloc_cache atomically.
>>
>> So add a in_softirq() debug checking in napi_consume_skb() to catch
>> this kind of error.
>>
>> Suggested-by: Eric Dumazet <eduma...@google.com>
>> Signed-off-by: Yunsheng Lin <linyunsh...@huawei.com>
>
>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>> index 1ba8f01..1834007 100644
>> --- a/net/core/skbuff.c
>> +++ b/net/core/skbuff.c
>> @@ -897,6 +897,10 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
>> return;
>> }
>>
>> + DEBUG_NET_WARN(!in_softirq(),
>> + "%s is called with non-zero budget outside softirq
>> context.\n",
>> + __func__);
>
> Can't we use lockdep instead of defining our own knobs?
>From the first look, using the below seems better than defining our
own knobs, because there is similar lockdep_assert_in_irq() checking
already and lockdep_assert_in_*() is NULL-OP when CONFIG_PROVE_LOCKING
is not defined.
>
> Like this maybe?
>
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index f5594879175a..5253a167d00c 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -594,6 +594,14 @@ do {
> \
> this_cpu_read(hardirqs_enabled))); \
> } while (0)
>
> +#define lockdep_assert_in_softirq() \
> +do { \
> + WARN_ON_ONCE(__lockdep_enabled && \
> + (softirq_count() == 0 || \
> + this_cpu_read(hardirq_context))); \
Using in_softirq() seems more obvious then using softirq_count()?
And there is below comment above avoiding the using of in_softirq(), maybe
that is why you use softirq_count() directly here?
"softirq_count() == 0" still mean we are not in the SoftIRQ context and
BH is not disabled. right? Perhap lockdep_assert_in_softirq_or_bh_disabled()
is more obvious?
/*
* Are we doing bottom half or hardware interrupt processing?
*
* in_irq() - We're in (hard) IRQ context
* in_softirq() - We have BH disabled, or are processing softirqs
* in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled
* in_serving_softirq() - We're in softirq context
* in_nmi() - We're in NMI context
* in_task() - We're in task context
*
* Note: due to the BH disabled confusion: in_softirq(),in_interrupt() really
* should not be used in new code.
*/
Also, is there any particular reason we do the "this_cpu_read(hardirq_context)"
checking?
Thanks.
> +} while (0)
>
>
>
>> if (!skb_unref(skb))
>> return;
>>
>
> .
>
