netdev - Re: [PATCH net-next] net: add in_softirq() debug checking in napi_consume

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Date:   Thu, 19 Nov 2020 12:41:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        linmiaohe@...wei.com, martin.varghese@...ia.com, pabeni@...hat.com,
        pshelar@....org, fw@...len.de, gnault@...hat.com,
        steffen.klassert@...unet.com, kyk.segfault@...il.com,
        viro@...iv.linux.org.uk, vladimir.oltean@....com,
        edumazet@...gle.com, saeed@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com
Subject: Re: [PATCH net-next] net: add in_softirq() debug checking in
 napi_consume_skb()

On Thu, Nov 19, 2020 at 05:19:44PM +0800, Yunsheng Lin wrote:
> On 2020/11/19 0:26, Jakub Kicinski wrote:
> > On Wed, 18 Nov 2020 16:57:57 +0100 Peter Zijlstra wrote:
> >> On Wed, Nov 18, 2020 at 07:43:48AM -0800, Jakub Kicinski wrote:
> >>
> >>> TBH the last sentence I wrote isn't clear even to me at this point ;D
> >>>
> >>> Maybe using just the macros from preempt.h - like this?
> >>>
> >>> #define lockdep_assert_in_softirq()                                    \
> >>> do {                                                                   \
> >>>        WARN_ON_ONCE(__lockdep_enabled                  &&              \
> >>>                     (!in_softirq() || in_irq() || in_nmi())	\
> >>> } while (0)
> 
> One thing I am not so sure about is the different irq context indicator
> in preempt.h and lockdep.h, for example lockdep_assert_in_irq() uses
> this_cpu_read(hardirq_context) in lockdep.h, and in_irq() uses
> current_thread_info()->preempt_count in preempt.h, if they are the same
> thing?

Very close, for more regular code they should be the same.