linux-kernel - Re: [PATCH 1/4] panic: Add panic_in

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Message-ID: <87v8y6wg7k.fsf@stepbren-lnx.us.oracle.com>
Date:   Wed, 26 Jan 2022 09:37:51 -0800
From:   Stephen Brennan <stephen.s.brennan@...cle.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] panic: Add panic_in_progress helper

Petr Mladek <pmladek@...e.com> writes:

> On Fri 2022-01-21 11:02:19, Stephen Brennan wrote:
>
> Please, add explanation why the new helper is added. It will be
> used in printk code to reduce risk of deadlocks during panic().
>
>> Suggested-by: Petr Mladek <pmladek@...e.com>
>> Signed-off-by: Stephen Brennan <stephen.s.brennan@...cle.com>
>> ---
>> We cannot define a static inline without including linux/atomic.h, so
>> I just added a macro for convenience in later patches. Since macros were
>> the only option, I didn't include a helper for
>> panic_in_progress_different_cpu().
>
> What is the exact problem with including atomic.h and using static
> inline, please?

Hi Petr,

linux/panic.h is a commonly included header, and so I didn't want to
pollute the namespaces of many other compilation units. (In fact, for
stable kernels we avoid changing headers to avoid changing the hashes
produced by genksyms). It could impact compile time too.

But I suppose I was prematurely optimizing. I can make them proper
static inlines instead :)

Stephen

>
> IMHO, the define is not a real solution. The macro won't be usable
> without including atomic.h. So, it would work only by chance.
>
> But it is possible that I miss something.
>
> Best Regards,
> Petr