linux-kernel - Re: [PATCH 1/2] pid: tighten pidmap spinlock critical section by removing kfree()

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Message-ID: <84144f020911230138v11b18709q28c186f9260f6d66@mail.gmail.com>
Date:	Mon, 23 Nov 2009 11:38:30 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	André Goddard Rosa <andre.goddard@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 1/2] pid: tighten pidmap spinlock critical section by 
	removing kfree()

(Adding some CC's.)

On Sat, Nov 21, 2009 at 2:16 PM, André Goddard Rosa
<andre.goddard@...il.com> wrote:
> Avoid calling kfree() under pidmap spinlock, calling it afterwards.
>
> Normally kfree() is very fast, but sometimes it can be slow, so avoid
> calling it under the spinlock if we can.
>
> Signed-off-by: André Goddard Rosa <andre.goddard@...il.com>
> cc: Pekka Enberg <penberg@...helsinki.fi>
> ---
>  kernel/pid.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/pid.c b/kernel/pid.c
> index d3f722d..55fd590 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -141,11 +141,12 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
>                         * installing it:
>                         */
>                        spin_lock_irq(&pidmap_lock);
> -                       if (map->page)
> -                               kfree(page);
> -                       else
> +                       if (!map->page) {
>                                map->page = page;
> +                               page = NULL;
> +                       }
>                        spin_unlock_irq(&pidmap_lock);
> +                       kfree(page);
>                        if (unlikely(!map->page))
>                                break;
>                }
> --
> 1.6.5.3.298.g39add
>
> --
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