linux-kernel - Re: [PATCH v2 1/2] mfd: syscon: add of_syscon_register

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Date: Thu, 20 Jun 2024 12:53:40 +0100
From: Peter Griffin <peter.griffin@...aro.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Lee Jones <lee@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>, 
	Alim Akhtar <alim.akhtar@...sung.com>, linux-arm-kernel@...ts.infradead.org, 
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tudor Ambarus <tudor.ambarus@...aro.org>, André Draszik <andre.draszik@...aro.org>, 
	Saravana Kannan <saravanak@...gle.com>, William McVicker <willmcvicker@...gle.com>, 
	Sam Protsenko <semen.protsenko@...aro.org>, kernel-team@...roid.com
Subject: Re: [PATCH v2 1/2] mfd: syscon: add of_syscon_register_regmap() API

Hi Arnd,

Thanks for the review feedback.

On Thu, 20 Jun 2024 at 12:40, Arnd Bergmann <arnd@...db.de> wrote:
>
>
> On Thu, Jun 20, 2024, at 13:24, Peter Griffin wrote:
> > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> > Reviewed-by: Arnd Bergmann <arnd@...db.de>
> > Reviewed-by: Sam Protsenko <semen.protsenko@...aro.org>
> > ---
> > Changes in v2:
> > - Keep syscon lock held between checking and adding entry (Krzysztof)
>
> Unfortunately you now have a different bug:
>
> > +     /* check if syscon entry already exists */
> > +     spin_lock(&syscon_list_slock);
> > +
> > +     list_for_each_entry(entry, &syscon_list, list)
> > +             if (entry->np == np) {
> > +                     syscon = entry;
> > +                     break;
> > +             }
> > +
> > +     if (syscon) {
> > +             ret = -EEXIST;
> > +             goto err_unlock;
> > +     }
> > +
> > +     syscon = kzalloc(sizeof(*syscon), GFP_KERNEL);
> > +     if (!syscon) {
> > +             ret = -ENOMEM;
> > +             goto err_unlock;
> > +     }
>
> You can't use GFP_KERNEL while holding a spinlock.
>
> I think the correct way to do this is to move the allocation
> before the locked section, and then free it in the failure case.

Thanks for spotting this! I'll update as you suggest in v3.

Peter.