linux-kernel - Re: [PATCH -v3 6/7] kexec jump: __ftrace_enabled

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Date:	Mon, 18 Aug 2008 09:18:13 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH -v3 6/7] kexec jump: __ftrace_enabled_save/restore

On Fri, 2008-08-15 at 14:49 +0200, Ingo Molnar wrote:
> * Huang Ying <ying.huang@...el.com> wrote:
> 
> > +/* Ftrace disable/restore without lock. Some synchronization mechanism
> > + * must be used to prevent ftrace_enabled to be changed between
> > + * disable/restore. */
> 
> use the proper comment style please:
> 
> /*
>  *
>  */

OK. I will change it.

> > +static inline int __ftrace_enabled_save(void)
> > +{
> > +#ifdef CONFIG_FTRACE
> > +	int saved_ftrace_enabled = ftrace_enabled;
> > +	ftrace_enabled = 0;
> > +	return saved_ftrace_enabled;
> > +#else
> > +	return 0;
> > +#endif
> > +}
> > +
> > +static inline void __ftrace_enabled_restore(int enabled)
> > +{
> > +#ifdef CONFIG_FTRACE
> > +	ftrace_enabled = enabled;
> > +#endif
> > +}
> 
> hm, what is this used for?
> 
> also, instead of such an ugly inline, why not create a proper 
> kernel/trace/* function for this. That would also give it access to all 
> the proper locking mechanisms - instead of relying on some extral 
> mechanism.

This function is used for kexec jump in machine_kexec(). Where all
non-boot CPUs and IRQ are disabled, system is going to kexec, and it is
not allowed to schedule to other process in this circumstance, so a
non-lock version is needed. A locked version has been implemented by
Steven Rostedt, I think it can be used for other circumstance.

Best Regards,
Huang Ying


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