linux-kernel - Re: [PATCH v3 0/5] Fix a whole host of nvmem registration/cleanup issues

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Message-ID: <Y7SWgC7m4tYSU1UJ@shell.armlinux.org.uk>
Date:   Tue, 3 Jan 2023 20:56:32 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Hector Martin <marcan@...can.st>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Gaosheng Cui <cuigaosheng1@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Maxime Ripard <mripard@...nel.org>
Subject: Re: [PATCH v3 0/5] Fix a whole host of nvmem registration/cleanup
 issues

Really not interested in your politics. Not interested in fixing this
problem.

I'll use these patches to fix the problem in my tree. I don't care about
mainline.

On Wed, Jan 04, 2023 at 03:12:44AM +0900, Hector Martin wrote:
> On 04/01/2023 01.58, Russell King (Oracle) wrote:
> > Hi,
> > 
> > This series fixes a whole host of nvmem registration/error cleanup
> > issues that have been identified by both Hector and myself. It is a
> > substantial rework of my original patch fixing the first problem.
> > 
> > The first most obvious problem is the race between nvmem registration
> > and use, which leads to sporadic failures of drivers to probe at boot
> > time.
> > 
> > While fixing this, it has been noticed that a recent fix to check the
> > return value of dev_set_name() introduced a new bug where wp_gpio was
> > not being put in that newly introduced error path.
> > 
> > Then there's a fix for a previous fix which itself purports to fix
> > another bug, but results in the allocated ID being leaked. Fix for a
> > fix for a fix is not good!
> > 
> > Then there's an error in the docbook documentation for wp_gpio (it's
> > listed as wp-gpio instead) but as nothing seems to set wp_gpio, we
> > might as well get rid of it - which also solves the issue that we
> > call gpiod_put() on this whether we own it or not.
> > 
> > Lastly, there's a fix for yet another spurious white-space in this
> > code, one of what seems to be a long history of past white-space
> > fixes.
> > 
> > These patches have been individually build-tested in the order of
> > posting, but not run-time tested except for the entire series.
> > 
> >  drivers/nvmem/core.c           | 51 ++++++++++++++++++------------------------
> >  include/linux/nvmem-provider.h |  2 --
> >  2 files changed, 22 insertions(+), 31 deletions(-)
> > 
> 
> Uhh. The series itself looks fine as far as fixing the problems, but I
> fail to see how this is any better than my attempt as far as backporting
> or commit atomicity goes. Patch #4 fixes the newer gpio leak bug *and*
> half fixes the race condition bug, then patch #5 completes the race
> condition fix but now depends on #4, meaning you're left with exactly
> the same backporting mess since now you can't apply #5 to older kernels
> and #4 only to newer ones. Splitting the commits like this buys you nothing.
> 
> I thought we were doing minimal backportable fixes to solve this, but
> your commit message for #4 literally says "While a minimal fix for this
> would be to add the gpiod_put() call, we can do better if we split
> device_register() [...]"... and then that whole "let's do better" part
> is what breaks the backportability again.
> 
> And then of course if you *do* manage to queue at least #4 to be
> backported to a newer subset of stable trees, #3 certainly isn't going
> to get backported itself (since it's just removing dead code, not
> eligible for stable since it fixes no actual bugs), but then you're left
> with the same
> broken-on-paper-except-nobody-uses-it-anyway-so-it-doesn't-matter
> situation my v2 left us in for those stable kernels.
> 
> That said, thanks for identifying that nobody uses the functionality I
> supposedly regressed (in a tiny corner case code path where it was
> already broken anyway) in my v2, and therefore I didn't actually regress
> anything in practice and strictly fixed real bugs.
> 
> - Hector
> 

-- 
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