linux-kernel - Re: [PATCH] bus: subsys: propagate errors from subsys interface's ->add

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Message-ID: <20150729233420.GA18070@kroah.com>
Date:	Wed, 29 Jul 2015 16:34:20 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, pi-cheng.chen@...aro.org
Subject: Re: [PATCH] bus: subsys: propagate errors from subsys interface's
 ->add_dev()

On Thu, Jul 30, 2015 at 01:29:01AM +0200, Rafael J. Wysocki wrote:
> On Wednesday, July 29, 2015 03:37:43 PM Greg KH wrote:
> > On Thu, Jul 30, 2015 at 01:01:21AM +0200, Rafael J. Wysocki wrote:
> > > On Wednesday, July 29, 2015 02:19:16 PM Greg KH wrote:
> > > > On Fri, Jun 26, 2015 at 02:32:47PM +0530, Viresh Kumar wrote:
> > > > > ->add_dev() may fail and the error returned from it can be useful for
> > > > > the caller.
> > > > > 
> > > > > For example, if some of the resources aren't ready yet and -EPROBE_DEFER
> > > > > is returned from ->add_dev(), then the owner of 'struct
> > > > > subsys_interface' may want to try probing again at a later point of
> > > > > time. And that requires a proper return value from ->add_dev().
> > > > > 
> > > > > Also, if we hit an error while registering subsys_interface, then we
> > > > > should stop proceeding further and rollback whatever has been done until
> > > > > then. Break part of subsys_interface_unregister() into another routine,
> > > > > which lets us call ->remove_dev() for all devices for which ->add_dev()
> > > > > is already called.
> > > > > 
> > > > > Cc: 3.3+ <stable@...r.kernel.org> # 3.3+
> > > > > Fixes: ca22e56debc5 ("driver-core: implement 'sysdev' functionality for regular devices and buses")
> > > > 
> > > > I don't see how this is a stable bug fix, what is resolved by it that
> > > > doesn't work today?  Is there some code that is expecting this
> > > > functionality that has never been present?
> > > > 
> > > > I'll go queue it up, but I don't think it is -stable material, but feel
> > > > free to change my mind.
> > > 
> > > There is a small problem with it that I've already pointed out to Viresh.
> > > 
> > > Namely, while changing subsys_interface_(un)register() to handle return
> > > values from ->add_dev(), it doesn't do the same thing in bus_probe_device()
> > > which I believe it should for consistency at least.
> > 
> > Oops, sorry, missed that response.  I'll go drop this patch then, thanks
> > for letting me know.
> > 
> > > But then, the question is whether or not the probing should fail and
> > > what if device_attach() returns 0 and one of the ->add_dev() callbacks
> > > returns an error.
> > 
> > That's a total mess...
> > 
> > Given that there are almost no uses of this api, I think people should
> > work it out before any more start to pop up :)
> 
> cpufreq is one of the users and that's where the problem is, but in my opinion
> it should be addressed in a different way.
> 
> But while we are at it, should the ->add_dev and ->remove_dev callbacks in
> struct subsys_interface return an int if their return values are always
> ignored?  Maybe it would be better to redefine them to be void to make it clear
> that they can't fail?

void makes sense to me.
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