linux-kernel - Re: [PATCH 2/5] mm: remove unlikly NULL from kfree

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Date:	Wed, 25 Mar 2009 09:34:13 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Steven Rostedt <srostedt@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 2/5] mm: remove unlikly NULL from kfree

On Wed, Mar 25, 2009 at 7:19 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
>
> Impact: clean up
>
> A NULL pointer to kfree is no longer unlikely, as seen by the
> annotated branch profiler:
>
>  correct incorrect  %        Function                  File              Line
>  ------- ---------  -        --------                  ----              ----
>  728571  1315540  64 kfree                          slab.c               3719
>
> This makes sense, since we now encourage developers to just call kfree
> without checking for NULL.

But those are _error handling paths_ (at least supposed to be). I
wonder which call-sites are responsible for this. Can frtrace help us
here?

> ---
>  mm/slab.c |    2 +-
>  mm/slob.c |    2 +-
>  mm/slub.c |    2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 4d00855..0386c33 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3716,7 +3716,7 @@ void kfree(const void *objp)
>        struct kmem_cache *c;
>        unsigned long flags;
>
> -       if (unlikely(ZERO_OR_NULL_PTR(objp)))
> +       if (ZERO_OR_NULL_PTR(objp))
>                return;
>        local_irq_save(flags);
>        kfree_debugcheck(objp);
> diff --git a/mm/slob.c b/mm/slob.c
> index 52bc8a2..e077174 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -491,7 +491,7 @@ void kfree(const void *block)
>  {
>        struct slob_page *sp;
>
> -       if (unlikely(ZERO_OR_NULL_PTR(block)))
> +       if (ZERO_OR_NULL_PTR(block))
>                return;
>
>        sp = (struct slob_page *)virt_to_page(block);
> diff --git a/mm/slub.c b/mm/slub.c
> index 0280eee..65dc436 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2743,7 +2743,7 @@ void kfree(const void *x)
>        struct page *page;
>        void *object = (void *)x;
>
> -       if (unlikely(ZERO_OR_NULL_PTR(x)))
> +       if (ZERO_OR_NULL_PTR(x))
>                return;
>
>        page = virt_to_head_page(x);
> --
> 1.6.2
>
> --
> --
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