linux-kernel - Re: [PATCH v2] net: phy: mdio-gpio: fix access that may sleep

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Date:   Wed, 14 Nov 2018 08:43:49 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        f.fainelli@...il.com, davem@...emloft.net
Subject: Re: [PATCH v2] net: phy: mdio-gpio: fix access that may sleep

On 2018-11-14 08:05, Andrew Lunn wrote:
> On Wed, Nov 14, 2018 at 07:37:03AM +0100, Martin Schiller wrote:
>> This commit re-enables support for slow GPIO pins. It was initially
>> introduced by commit
>> 	2d6c9091ab7630dfcf34417c6683ce4764d7d40a
>> and got lost by commit
>> 	7e5fbd1e0700f1bdb94508f84ec2aeb01eed7b12
> 
> Hi Martin
> 
> Was it really lost? It looks like _cansleep() just adds an extra check
> might_sleep_if(extra_checks), but it does not change any
> functionality.

Well, you are right, the functionality itself is not broken, but using
the NON _cansleep() functions on GPIOs that have the cansleep flag set,
this leads to a lot of kernel warnings/backtraces which makes the system
in fact useless.

Thats the WARN_ON() here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?h=v4.20-rc2#n2992

and here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?h=v4.20-rc2#n3304

> 
> So the change itself is O.K, i'm just not too sure about the commit
> message.
> 
> 	Andrew

Hmm, ok. What would you suggest for a better commit message?

I thought it would be helpful to know that this was already in there
and got (inadvertently?) removed by another commit.

Martin