linux-kernel - Re: [PATCH 1/1] tty: vt: Remove redundant null check before kfree.

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Message-ID: <20121121151604.GA21983@kroah.com>
Date:	Wed, 21 Nov 2012 07:16:05 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Sachin Kamat <sachin.kamat@...aro.org>
Cc:	linux-kernel@...r.kernel.org, patches@...aro.org
Subject: Re: [PATCH 1/1] tty: vt: Remove redundant null check before kfree.

On Wed, Nov 21, 2012 at 08:21:40PM +0530, Sachin Kamat wrote:
> On 21 November 2012 20:16, Greg KH <gregkh@...uxfoundation.org> wrote:
> > On Wed, Nov 21, 2012 at 10:49:07AM +0530, Sachin Kamat wrote:
> >> kfree on a NULL pointer is a no-op.
> >>
> >> Signed-off-by: Sachin Kamat <sachin.kamat@...aro.org>
> >> ---
> >>  drivers/tty/vt/consolemap.c |    6 ++----
> >>  1 files changed, 2 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
> >> index 2aaa0c2..248381b 100644
> >> --- a/drivers/tty/vt/consolemap.c
> >> +++ b/drivers/tty/vt/consolemap.c
> >> @@ -410,10 +410,8 @@ static void con_release_unimap(struct uni_pagedir *p)
> >>               kfree(p->inverse_translations[i]);
> >>               p->inverse_translations[i] = NULL;
> >>       }
> >> -     if (p->inverse_trans_unicode) {
> >> -             kfree(p->inverse_trans_unicode);
> >> -             p->inverse_trans_unicode = NULL;
> >> -     }
> >> +     kfree(p->inverse_trans_unicode);
> >> +     p->inverse_trans_unicode = NULL;
> >
> > kfree with NULL is a no-op, but the line after that just caused a kernel
> > crash if it was NULL, so I can't accept this type of thing.
> >
> > Please be more careful.
> 
> My mistake. Apologies for the same.
> 
> Do we need to assign the pointer to NULL after freeing?

It depends if it is checked later on, is it?

> > What's with the patches@...aro.org email address?  What is that for?
> That is a logging mechanism (done by patchwork) for all patches sent
> by Linaro engineers.

So you can track it internally?  Why?

greg k-h
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