linux-kernel - Re: [PATCH v1 1/1] ACPI: utils: Fix reference counting in for_each_acpi_dev

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Date:   Wed, 26 May 2021 11:35:13 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Daniel Scally <djrscally@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Yong Zhi <yong.zhi@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Tianshu Qiu <tian.shu.qiu@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>
Subject: Re: [PATCH v1 1/1] ACPI: utils: Fix reference counting in for_each_acpi_dev_match()

On Wed, May 26, 2021 at 1:29 AM Daniel Scally <djrscally@...il.com> wrote:
> On 20/05/2021 20:40, Rafael J. Wysocki wrote:
> > On Thu, May 20, 2021 at 9:13 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> >> On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko
> >> <andy.shevchenko@...il.com> wrote:
> >>> Currently it's possible to iterate over the dangling pointer in case the device
> >>> suddenly disappears. This may happen becase callers put it at the end of a loop.
> >>>
> >>> Instead, let's move that call inside acpi_dev_get_next_match_dev().
> >> Not really.
> > OK, I see what you want to achieve and the macro is actually buggy,
> > because it leaves unbalanced references behind.
>
>
> Yeah; I guess the originally intended use (which was "get all these
> devices") doesn't really tally with the naming or with the operation of
> similar functions in the kernel like the fwnode_handle ops; sorry about
> that. Anyway; I think Andy's fix is the right way to do it, so the
> calling code's responsible for holding onto a reference if it wants to
> keep it.

I think we need to postpone the fix till v5.14-rc1 is out. It appears
that some code has been changed in EFI and media subsystems so that
patch will be in conflict with.


-- 
With Best Regards,
Andy Shevchenko