linux-kernel - Re: [PATCH] idr: fix a critical misallocation bug, take#2

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Date:	Fri, 12 Feb 2010 08:36:23 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>, Eric Paris <eparis@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Xiaotian Feng <xtfeng@...il.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: Re: [PATCH] idr: fix a critical misallocation bug, take#2

Quoting Tejun Heo (tj@...nel.org):
> This is retry of reverted 859ddf09743a8cc680af33f7259ccd0fd36bfe9d
> which contained two bugs.
> 
> * pa[idp->layers] should be cleared even if it's not used by
>   sub_alloc() because it's used by mark idr_mark_full().
> 
> * The original condition check also assigned pa[l] to p which the new
>   code didn't do thus leaving p pointing at the wrong layer.
> 
> Both problems have been fixed and the idr code has received good
> amount testing using userland testing setup where simple bitmap
> allocator is run parallel to verify the result of idr allocation.
> 
> The bug this patch fixes is caused by sub_alloc() optimization path
> bypassing out-of-room condition check and restarting allocation loop
> with starting value higher than maximum allowed value.  For detailed
> description, please read commit message of 859ddf09.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Based-on-patch-from: Eric Paris <eparis@...hat.com>
> Reported-by: Eric Paris <eparis@...hat.com>
> Tested-by: Stefan Lippers-Hollmann <s.l-h@....de>

Full LTP still running, but this passes semget05 which is what
crashed the last version.  So that's

Tested-by: Serge Hallyn <serue@...ibm.com>

> ---
> Heh... Embarrassingly, it turns out Eric's original patch is correct
> and all I did was adding two mistakes. :-) I'm pretty sure this is the
> correct fix and have tested it quite extensively.  But, given the
> fragility of this thing, Andrew, can you please put it in your tree
> and push it after 2.6.33 merge window opens?  Greg, please don't put
> this into -stable until at least 2.6.33-rc2 seems okay.
> 
> Thank you.
> 
>  lib/idr.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/idr.c b/lib/idr.c
> index 1cac726..0dc7822 100644
> --- a/lib/idr.c
> +++ b/lib/idr.c
> @@ -156,10 +156,12 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
>  			id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;
> 
>  			/* if already at the top layer, we need to grow */
> -			if (!(p = pa[l])) {
> +			if (id >= 1 << (idp->layers * IDR_BITS)) {
>  				*starting_id = id;
>  				return IDR_NEED_TO_GROW;
>  			}
> +			p = pa[l];
> +			BUG_ON(!p);
> 
>  			/* If we need to go up one layer, continue the
>  			 * loop; otherwise, restart from the top.
--
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