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

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Date:   Wed, 14 Nov 2018 21:46:54 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Martin Schiller <ms@....tdt.de>
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 Wed, Nov 14, 2018 at 08:43:49AM +0100, Martin Schiller wrote:
> 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

Hi Martin

Right, this is really what you are fixing. So the commit message
should talk about these WARN_ON being hit.

> >
> >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?

Up until commit XXX, the _cansleep variants of the gpio_ API was
used. After that commit and the change to gpiod_ API, the _cansleep()
was dropped. This then results in WARN_ON() when used with GPIO
devices which do sleep. Add back the _cansleep() to avoid this.

This is something which is useful in stable. So please base this fix
on DaveM net tree, not net-next, and include a Fixes: tag for the
patch which broke it.

      Thanks
	Andrew