linux-kernel - Re: [PATCH v13 03/10] mux: minimal mux subsystem and gpio-based mux controller

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Date:   Sat, 22 Apr 2017 01:28:28 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, Wolfram Sang <wsa@...-dreams.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jonathan Corbet <corbet@....net>, <linux-i2c@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <linux-doc@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Ian King <colin.king@...onical.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Philipp Zabel <p.zabel@...gutronix.de>, <kernel@...gutronix.de>
Subject: Re: [PATCH v13 03/10] mux: minimal mux subsystem and gpio-based mux
 controller

On 2017-04-20 23:53, Peter Rosin wrote:
> On 2017-04-18 23:53, Peter Rosin wrote:
>> On 2017-04-18 13:44, Greg Kroah-Hartman wrote:
>>> On Tue, Apr 18, 2017 at 12:59:50PM +0200, Peter Rosin wrote:
>>>> On 2017-04-18 10:51, Greg Kroah-Hartman wrote:
>>>>> On Thu, Apr 13, 2017 at 06:43:07PM +0200, Peter Rosin wrote:
> 
> *snip*
> 
>>>>>> +	if (mux->idle_state != MUX_IDLE_AS_IS &&
>>>>>> +	    mux->idle_state != mux->cached_state)
>>>>>> +		ret = mux_control_set(mux, mux->idle_state);
>>>>>> +
>>>>>> +	up_read(&mux->lock);
>>>>>
>>>>> You require a lock to be held for a "global" function?  Without
>>>>> documentation?  Or even a sparse marking?  That's asking for trouble...
>>>>
>>>> Documentation I can handle, but where should I look to understand how I
>>>> should add sparse markings?
>>>
>>> Run sparse on the code and see what it says :)
>>
>> Will do.
> 
> I just did, and even went through the trouble of getting the bleeding
> edge sparse from the git repo when sparse 0.5.0 came up empty, but it's
> all silence for me. So, how do I add sparse markings?

I looked some more into this, and the markings I find that seem related
are __acquire() and __release(). But neither mutex_lock() nor up_read()
has markings like that, so adding them when using those kinds of locks
in an imbalanced way seems like a sure way of *getting* sparse messages
about context imbalance...

So, either that, or you are talking about __must_check markings?

I feel like I'm missing something, please advise further.

Cheers,
peda