Re: [PATCH 1/2] pid: tighten pidmap spinlock critical section by removing kfree()
From: Pekka Enberg
Date: Mon Nov 23 2009 - 04:38:36 EST
(Adding some CC's.)
On Sat, Nov 21, 2009 at 2:16 PM, André Goddard Rosa
<andre.goddard@xxxxxxxxx> 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@xxxxxxxxx>
> cc: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> ---
> 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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