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

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Date:   Fri, 30 Oct 2020 12:58:34 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH] devres: zero the memory in devm_krealloc() if needed

On Fri, Oct 30, 2020 at 12:57:06PM +0200, Andy Shevchenko wrote:
> On Fri, Oct 30, 2020 at 10:03:50AM +0100, Bartosz Golaszewski wrote:
> > On Thu, Oct 29, 2020 at 9:05 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > >
> > > On Mon, Oct 26, 2020 at 01:27:28PM +0100, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > > >
> > > > If we're returning the same pointer (when new size is smaller or equal
> > > > to the old size) we need to check if the user wants the memory zeroed
> > > > and memset() it manually if so.
> > >
> > > 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.

Two notes:
 - perhaps kzrealloc() for what you want
 - there is a library call reallocarray() which supports your idea about
   krealloc_array() API in kernel.


-- 
With Best Regards,
Andy Shevchenko