linux-kernel - Re: [PATCH] lib/idr.c: Fix bug introduced by RCU fix

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Message-ID: <21d7e9970812101546n40ba9043r8fdf35b986c5d377@mail.gmail.com>
Date:	Thu, 11 Dec 2008 09:46:12 +1000
From:	"Dave Airlie" <airlied@...il.com>
To:	"Manfred Spraul" <manfred@...orfullife.com>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	cebbert@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] lib/idr.c: Fix bug introduced by RCU fix

On Thu, Dec 11, 2008 at 3:17 AM, Manfred Spraul
<manfred@...orfullife.com> wrote:
> The last patch to lib/idr.c caused a bug if idr_get_new_above() was
> called on an empty idr:
> Usually, nodes stay on the same layer. New layers are added to the top
> of the tree.
> The exception is idr_get_new_above() on an empty tree: In this case,
> the new root node is first added on layer 0, then moved upwards.
> p->layer was not updated.
>
> As usual: You shall never rely on the source code comments, they
> will only mislead you.
>
> Signed-off-by: Manfred Spraul <manfred@...orfullife.com>

I've given this a run on my dri system and it appears to work great.

Tested-by: Dave Airlie <airlied@...hat.com>


> ---
>  lib/idr.c |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/lib/idr.c b/lib/idr.c
> index 7a785a0..1c4f928 100644
> --- a/lib/idr.c
> +++ b/lib/idr.c
> @@ -220,8 +220,14 @@ build_up:
>         */
>        while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
>                layers++;
> -               if (!p->count)
> +               if (!p->count) {
> +                       /* special case: if the tree is currently empty,
> +                        * then we grow the tree by moving the top node
> +                        * upwards.
> +                        */
> +                       p->layer++;
>                        continue;
> +               }
>                if (!(new = get_from_free_list(idp))) {
>                        /*
>                         * The allocation failed.  If we built part of
> --
> 1.5.6.5
>
>
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