linux-kernel - Re: [PATCH v1 1/1] platform/x86: ideapad-laptop: Make the scope

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Message-ID: <Ztcn2Yu2TNSOYbhP@smile.fi.intel.com>
Date: Tue, 3 Sep 2024 18:14:33 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Gergo Koteles <soyer@....hu>
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Hans de Goede <hdegoede@...hat.com>,
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ike Panhc <ike.pan@...onical.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v1 1/1] platform/x86: ideapad-laptop: Make the
 scope_guard() clear of its scope

On Tue, Sep 03, 2024 at 05:00:51PM +0200, Gergo Koteles wrote:
> On Thu, 2024-08-29 at 19:50 +0300, Andy Shevchenko wrote:
> > First of all, it's a bit counterintuitive to have something like
> > 
> > 	int err;
> > 	...
> > 	scoped_guard(...)
> > 		err = foo(...);
> > 	if (err)
> > 		return err;
> > 
> > Second, with a particular kernel configuration and compiler version in
> > one of such cases the objtool is not happy:
> > 
> >   ideapad-laptop.o: warning: objtool: .text.fan_mode_show: unexpected end of section
> > 
> > I'm not an expert on all this, but the theory is that compiler and
> > linker in this case can't understand that 'result' variable will be
> > always initialized as long as no error has been returned. Assigning
> > 'result' to a dummy value helps with this. Note, that fixing the
> > scoped_guard() scope (as per above) does not make issue gone.
> > 
> > That said, assign dummy value and make the scope_guard() clear of its scope.
> > For the sake of consistency do it in the entire file.
> > 
> 
> Interestingly, if I open a scope manually and use the plain guard, the
> warning disappears.

Yes, that's what I also have, but I avoid that approach because in that case
the printing will be done inside the lock, widening the critical section for
no benefits.

> 	...
> 	unsigned long result;
> 	int err;
> 
> 	{
> 		guard(mutex)(&priv->vpc_mutex);
> 		err = read_ec_data(priv->adev->handle, VPCCMD_R_FAN,
> &result);
> 		if (err)
> 			return err;
> 	}
> 	...
> 
> This looks a bit strange, but is probably easier for the compiler than
> the for loop of scoped_guard.
> 
> But I don't know how well this style fits into the kernel.

-- 
With Best Regards,
Andy Shevchenko