linux-kernel - Re: [PATCH v2] nvmem: core: Fix race in nvmem

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Message-ID: <Y7RIMeMoKD70NIcc@shell.armlinux.org.uk>
Date:   Tue, 3 Jan 2023 15:22:25 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Hector Martin <marcan@...can.st>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        asahi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Eric Curtin <ecurtin@...hat.com>
Subject: Re: [PATCH v2] nvmem: core: Fix race in nvmem_register()

On Wed, Jan 04, 2023 at 12:14:10AM +0900, Hector Martin wrote:
> On 04/01/2023 00.06, Russell King (Oracle) wrote:
> > Hi Hector,
> > 
> > On Tue, Jan 03, 2023 at 10:48:52PM +0900, Hector Martin wrote:
> >>>> @@ -822,11 +822,8 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >>>>   		break;
> >>>>   	}
> >>>>
> >>>> -	if (rval) {
> >>>> -		ida_free(&nvmem_ida, nvmem->id);
> >>>> -		kfree(nvmem);
> >>>> -		return ERR_PTR(rval);
> >>>> -	}
> >>>> +	if (rval)
> >>>> +		goto err_gpiod_put;
> >>>
> >>> Why was gpiod changes added to this patch, that should be a separate 
> >>> patch/discussion, as this is not relevant to the issue that you are 
> >>> reporting.
> >>
> >> Because freeing the device also does a gpiod_put in the destructor, so
> >> doing this is correct in every other instance below and maintains
> >> existing behavior, and it just so happens that this instance converges
> >> into the same codepath so it is correct to merge it, and it just so
> >> happens that the gpiod put was missing in this path to begin with so
> >> this becomes a drive-by bugfix.
> >>
> >> If you don't like it I can remove it (i.e. reintroduce the bug for no
> >> good reason) and you can submit this fix yourself, because I have no
> >> incentive to waste time submitting a separate patch to fix a GPIO leak
> >> in an error path corner case in a subsystem I don't own and I have much
> >> bigger things to spend my (increasingly lower and lower) willingness to
> >> fight for upstream submissions than this.
> >>
> >> Seriously, what is wrong with y'all kernel people. No other open source
> >> project wastes contributors' time with stupid nitpicks like this. I
> >> found a bug, I fixed it, I then fixed the issues you pointed out, and I
> >> don't have the time nor energy to fight over this kind of nonsense next.
> >> Do you want bugs fixed or not?
> > 
> > This is not nonsense. We have always had a policy of one fix/change
> > per patch, and in this case it makes complete and utter sense. Of
> > course, the interpretation of "one change" is a matter of opinion.
> 
> The change here is the race condition fix. That change involves adding
> an error cleanup path that involves a gpio_put(). Therefore it seems
> logical to actually use it in that one extra case that should've used it
> anyway, a few lines above.

The two are entirely unrelated. as I've already explained. The call
to device_register() happens _after_ the check for rval from the
dev_set_name() that you are changing. Moving device_register() doesn't
make the lack of gpiod_put() any better or worse than it was before.

That said, I'm now thinking that my patch is actually wrong, but for
a different reason unrelated to the gpiod issue. :(

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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