Re: [PATCH net-next] net: add in_softirq() debug checking in napi_consume_skb()
From: Yunsheng Lin <hidden>
Date: 2020-11-02 03:14:45
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On 2020/11/1 6:38, Jakub Kicinski wrote:
On Thu, 29 Oct 2020 19:34:48 +0800 Yunsheng Lin wrote:quoted
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 <edumazet@google.com> Signed-off-by: Yunsheng Lin <redacted>quoted
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.
quoted hunk ↗ jump to hunk
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)quoted
if (!skb_unref(skb)) return;.