linux-kernel - Re: [PATCH v1 1/4] spidev: Do not use atomic bit operations when allocating minor

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Message-ID: <YjtXbDyCWZxKnf4Y@smile.fi.intel.com>
Date:   Wed, 23 Mar 2022 19:22:52 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/4] spidev: Do not use atomic bit operations when
 allocating minor

On Wed, Mar 23, 2022 at 04:39:01PM +0000, Mark Brown wrote:
> On Wed, Mar 23, 2022 at 04:02:12PM +0200, Andy Shevchenko wrote:
> > There is no need to use atomic bit operations when allocating a minor
> > number since it's done under a mutex. Moreover, one of the operations
> > that is in use is non-atomic anyway.

...

> >  	if (status == 0) {
> > -		set_bit(minor, minors);
> > +		__set_bit(minor, minors);
> >  		list_add(&spidev->device_entry, &device_list);
> 
> There's no *need* but the __ looks suspicious...  what's the upside
> here?

It's exactly what is written in the commit message

__*_bit() are non-atomic
*_bit() are atomic

Since they are wrapped by mutex, the atomic ones are not needed.

-- 
With Best Regards,
Andy Shevchenko