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SubjectRe: [PATCH] idr: fix a critical misallocation bug, take#2
Quoting Tejun Heo (tj@kernel.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@kernel.org>
> Based-on-patch-from: Eric Paris <eparis@redhat.com>
> Reported-by: Eric Paris <eparis@redhat.com>
> Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>

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

Tested-by: Serge Hallyn <serue@us.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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