linux-kernel - Re: [PATCH] devres: zero the memory in devm

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Date:   Fri, 30 Oct 2020 13:21:00 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devres: zero the memory in devm_krealloc() if needed

On Fri, Oct 30, 2020 at 12:03 PM Bartosz Golaszewski
<bgolaszewski@...libre.com> wrote:
>
> On Fri, Oct 30, 2020 at 11:56 AM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
>
> [snip]
>
> > > >
> > > > Any use case? Because to me it sounds contradictory to the whole idea of [k]realloc().
> > >
> > > This is kind of a gray area in original krealloc() too and I want to
> > > submit a patch for mm too. Right now krealloc ignores the __GFP_ZERO
> > > flag if new_size <= old_size but zeroes the memory if new_size >
> > > old_size.
> >
> > > This should be consistent - either ignore __GFP_ZERO or
> > > don't ignore it in both cases. I think that not ignoring it is better
> > > - if user passes it then it's for a reason.
> >
> > Sorry, but I consider in these two choices the best is the former one, i.e.
> > ignoring, because non-ignoring for sizes less than current is counter the
> > REalloc() by definition.
> >
> > Reading realloc(3):
> >
> > "If the new size is larger than the old size, the added memory will not be
> > initialized."
> >
> > So, supports my choice over yours.
>
> Kernel memory management API is not really orthogonal to the one in
> user-space. For example: kmalloc() takes the gfp parameter and if you
> pass __GFP_ZERO to it, it zeroes the memory even if user-space
> malloc() never does.
>

Ok so I was wrong - it turns out that krealloc() is consistent in
ignoring __GFP_ZERO after all. In that case this patch can be dropped.

Bartosz