linux-kernel - Re: [PATCH v3 1/3] devres: provide devm

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Message-ID: <CAMpxmJXjhzYr5djfn5K9yxCOohtB76bbgY+Sh1ZLNzF7c0Gzmg@mail.gmail.com>
Date:   Sun, 12 Jul 2020 10:19:09 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        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 Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] devres: provide devm_krealloc()

On Sat, Jul 11, 2020 at 5:08 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Fri, Jul 10, 2020 at 7:17 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >
> > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >
> > Implement the managed variant of krealloc(). This function works with
> > all memory allocated by devm_kmalloc() (or devres functions using it
> > implicitly like devm_kmemdup(), devm_kstrdup() etc.).
> >
> > Managed realloc'ed chunks can be manually released with devm_kfree().
>
> ...
>
> >    devm_kfree()
> >    devm_kmalloc()
> >    devm_kmalloc_array()
> > +  devm_krealloc()
> >    devm_kmemdup()
> >    devm_kstrdup()
> >    devm_kvasprintf()
>
> Order?
>

I didn't notice these were ordered alphabetically, I thought it was by
functionality.

> ...
>
> > +void *devm_krealloc(struct device *dev, void *ptr, size_t new_size, gfp_t gfp)
>
> Do we really need the 'new_' prefix in the parameter?
>

Yes, I think this is a good name for a function that's meant to modify
the size of a memory chunk.

> > +{
> > +       struct devres *old_dr, *new_dr;
> > +       struct list_head old_head;
> > +       unsigned long flags;
> > +       void *ret = NULL;
> > +       size_t tot_size;
>
> tot -> total.
>

Meh, ok.

> > +
> > +       if (unlikely(!new_size)) {
> > +               devm_kfree(dev, ptr);
> > +               return ZERO_SIZE_PTR;
> > +       }
>
> I guess here we need a comment of the possibilities below to have
> ZERO_SIZE_PTR as input.
>

Better yet: I'll just add a kernel doc for this function.

> > +       if (unlikely(ZERO_OR_NULL_PTR(ptr)))
> > +               return devm_kmalloc(dev, new_size, gfp);
> > +
> > +       if (WARN_ON(is_kernel_rodata((unsigned long)ptr)))
> > +               /*
> > +                * We cannot reliably realloc a const string returned by
> > +                * devm_kstrdup_const().
> > +                */
> > +               return NULL;
> > +
> > +       if (!check_dr_size(new_size, &tot_size))
> > +               return NULL;
> > +
> > +       spin_lock_irqsave(&dev->devres_lock, flags);
> > +
> > +       old_dr = find_dr(dev, devm_kmalloc_release, devm_kmalloc_match, ptr);
>
> > +       if (WARN_ON(!old_dr))
>
> Under spin lock? I would rather see spin unlock followed by WARN.
>

Yeah, can be done.

> > +               /* Memory chunk not managed or managed by a different device. */
> > +               goto out;
> > +
> > +       old_head = old_dr->node.entry;
> > +
> > +       new_dr = krealloc(old_dr, tot_size, gfp);
> > +       if (!new_dr)
> > +               goto out;
> > +
> > +       if (new_dr != old_dr)
> > +               list_replace(&old_head, &new_dr->node.entry);
> > +
> > +       ret = new_dr->data;
> > +
> > +out:
> > +       spin_unlock_irqrestore(&dev->devres_lock, flags);
> > +       return ret;
> > +}
>
> --
> With Best Regards,
> Andy Shevchenko

Bartosz