linux-kernel - Re: [PATCH v7 1/3] devres: provide devm

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Message-ID: <20200818082500.GB1891694@smile.fi.intel.com>
Date:   Tue, 18 Aug 2020 11:25:00 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Michal Simek <michal.simek@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v7 1/3] devres: provide devm_krealloc()

On Mon, Aug 17, 2020 at 10:02:05PM +0200, Bartosz Golaszewski wrote:
> On Mon, Aug 17, 2020 at 7:43 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > On Mon, Aug 17, 2020 at 07:05:33PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>

...

> > > +static struct devres *to_devres(void *data)
> > > +{
> > > +     return (struct devres *)((u8 *)data - ALIGN(sizeof(struct devres),
> > > +                                                 ARCH_KMALLOC_MINALIGN));
> >
> > Do you really need both explicit castings?
> >
> 
> Yeah, we can probably drop the (struct devres *) here.

void * -> u8 * here is also not needed, it is considered byte access IIRC.

> > > +}

...

> >  - hasn't gone while you run a ksize()?

> At some point you need to draw a line. In the end: how do you
> guarantee a devres buffer hasn't been freed when you're using it? In
> my comment to the previous version of this patch I clarified that we
> need to protect all modifications of the devres linked list - we must
> not realloc a chunk that contains the links without taking the
> spinlock but also we must not call alloc() funcs with GFP_KERNEL with
> spinlock taken. The issue we could run into is: someone modifies the
> linked list by adding/removing other managed resources, not modifying
> this one.
> 
> The way this function works now guarantees it but other than that:
> it's up to the users to not free memory they're actively using.

Thanks for clarification. I agree.

-- 
With Best Regards,
Andy Shevchenko