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Message-ID: <20130304173714.GE9031@hercules>
Date: Mon, 4 Mar 2013 17:37:14 +0000
From: Luis Henriques <luis.henriques@...onical.com>
To: Ben Hutchings <ben@...adent.org.uk>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
akpm@...ux-foundation.org, Tejun Heo <tj@...nel.org>,
Rusty Russell <rusty@...tcorp.com.au>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [ 114/153] idr: fix top layer handling
On Mon, Mar 04, 2013 at 03:39:01AM +0000, Ben Hutchings wrote:
> 3.2-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Tejun Heo <tj@...nel.org>
>
> commit 326cf0f0f308933c10236280a322031f0097205d upstream.
>
> Most functions in idr fail to deal with the high bits when the idr
> tree grows to the maximum height.
>
> * idr_get_empty_slot() stops growing idr tree once the depth reaches
> MAX_IDR_LEVEL - 1, which is one depth shallower than necessary to
> cover the whole range. The function doesn't even notice that it
> didn't grow the tree enough and ends up allocating the wrong ID
> given sufficiently high @starting_id.
>
> For example, on 64 bit, if the starting id is 0x7fffff01,
> idr_get_empty_slot() will grow the tree 5 layer deep, which only
> covers the 30 bits and then proceed to allocate as if the bit 30
> wasn't specified. It ends up allocating 0x3fffff01 without the bit
> 30 but still returns 0x7fffff01.
>
> * __idr_remove_all() will not remove anything if the tree is fully
> grown.
>
> * idr_find() can't find anything if the tree is fully grown.
>
> * idr_for_each() and idr_get_next() can't iterate anything if the tree
> is fully grown.
>
> Fix it by introducing idr_max() which returns the maximum possible ID
> given the depth of tree and replacing the id limit checks in all
> affected places.
>
> As the idr_layer pointer array pa[] needs to be 1 larger than the
> maximum depth, enlarge pa[] arrays by one.
>
> While this plugs the discovered issues, the whole code base is
> horrible and in desparate need of rewrite. It's fragile like hell,
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> [bwh: Backported to 3.2:
> - Adjust context
> - s/MAX_IDR_LEVEL/MAX_LEVEL/; s/MAX_IDR_SHIFT/MAX_ID_SHIFT/
> - Drop change to idr_alloc()]
> Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> ---
> lib/idr.c | 38 +++++++++++++++++++++++---------------
> 1 file changed, 23 insertions(+), 15 deletions(-)
>
> --- a/lib/idr.c
> +++ b/lib/idr.c
> @@ -39,6 +39,14 @@
> static struct kmem_cache *idr_layer_cache;
> static DEFINE_SPINLOCK(simple_ida_lock);
>
> +/* the maximum ID which can be allocated given idr->layers */
> +static int idr_max(int layers)
> +{
> + int bits = min_t(int, layers * IDR_BITS, MAX_ID_SHIFT);
> +
> + return (1 << bits) - 1;
> +}
> +
> static struct idr_layer *get_from_free_list(struct idr *idp)
> {
> struct idr_layer *p;
> @@ -223,7 +231,7 @@ build_up:
> * Add a new layer to the top of the tree if the requested
> * id is larger than the currently allocated space.
> */
> - while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
> + while (id > idr_max(layers)) {
> layers++;
> if (!p->count) {
> /* special case: if the tree is currently empty,
> @@ -265,7 +273,7 @@ build_up:
>
> static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
> {
> - struct idr_layer *pa[MAX_LEVEL];
> + struct idr_layer *pa[MAX_LEVEL + 1];
> int id;
>
> id = idr_get_empty_slot(idp, starting_id, pa);
> @@ -357,7 +365,7 @@ static void idr_remove_warning(int id)
> static void sub_remove(struct idr *idp, int shift, int id)
> {
> struct idr_layer *p = idp->top;
> - struct idr_layer **pa[MAX_LEVEL];
> + struct idr_layer **pa[MAX_LEVEL + 1];
> struct idr_layer ***paa = &pa[0];
> struct idr_layer *to_free;
> int n;
> @@ -451,16 +459,16 @@ void idr_remove_all(struct idr *idp)
> int n, id, max;
> int bt_mask;
> struct idr_layer *p;
> - struct idr_layer *pa[MAX_LEVEL];
> + struct idr_layer *pa[MAX_LEVEL + 1];
> struct idr_layer **paa = &pa[0];
>
> n = idp->layers * IDR_BITS;
> p = idp->top;
> rcu_assign_pointer(idp->top, NULL);
> - max = 1 << n;
> + max = idr_max(idp->layers);
>
> id = 0;
> - while (id < max) {
> + while (id >= 0 && id <= max) {
> while (n > IDR_BITS && p) {
> n -= IDR_BITS;
> *paa++ = p;
> @@ -519,7 +527,7 @@ void *idr_find(struct idr *idp, int id)
> /* Mask off upper bits we don't use for the search. */
> id &= MAX_ID_MASK;
>
> - if (id >= (1 << n))
> + if (id > idr_max(p->layer + 1))
> return NULL;
> BUG_ON(n == 0);
>
> @@ -555,15 +563,15 @@ int idr_for_each(struct idr *idp,
> {
> int n, id, max, error = 0;
> struct idr_layer *p;
> - struct idr_layer *pa[MAX_LEVEL];
> + struct idr_layer *pa[MAX_LEVEL + 1];
> struct idr_layer **paa = &pa[0];
>
> n = idp->layers * IDR_BITS;
> p = rcu_dereference_raw(idp->top);
> - max = 1 << n;
> + max = idr_max(idp->layers);
>
> id = 0;
> - while (id < max) {
> + while (id >= 0 && id <= max) {
> while (n > 0 && p) {
> n -= IDR_BITS;
> *paa++ = p;
> @@ -601,7 +609,7 @@ EXPORT_SYMBOL(idr_for_each);
> */
> void *idr_get_next(struct idr *idp, int *nextidp)
> {
> - struct idr_layer *p, *pa[MAX_LEVEL];
> + struct idr_layer *p, *pa[MAX_LEVEL + 1];
> struct idr_layer **paa = &pa[0];
> int id = *nextidp;
> int n, max;
> @@ -611,9 +619,9 @@ void *idr_get_next(struct idr *idp, int
> if (!p)
> return NULL;
> n = (p->layer + 1) * IDR_BITS;
> - max = 1 << n;
> + max = idr_max(p->layer + 1);
>
> - while (id < max) {
> + while (id >= 0 && id <= max) {
> while (n > 0 && p) {
> n -= IDR_BITS;
> *paa++ = p;
> @@ -787,7 +795,7 @@ EXPORT_SYMBOL(ida_pre_get);
> */
> int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
> {
> - struct idr_layer *pa[MAX_LEVEL];
> + struct idr_layer *pa[MAX_LEVEL + 1];
> struct ida_bitmap *bitmap;
> unsigned long flags;
> int idr_id = starting_id / IDA_BITMAP_BITS;
>
>
> --
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I've reviewed this backport and it looks correct to me. I've queued it
in the 3.5 tree as well.
Cheers,
--
Luis
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