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From: Eric Dumazet on 24 Mar 2010 17:30
Le mercredi 24 mars 2010 à 16:14 -0500, Christoph Lameter a écrit :
> Here is a patch for the second case. I think its better since it results
> in an error display and it avoids the alloc for each slab. Add this piece
> to your patch?
>
> Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>

Sure, here is third version :

Thanks

[PATCH] slub: Potential stack overflow

I discovered that we can overflow stack if CONFIG_SLUB_DEBUG=y and use
slabs with many objects, since list_slab_objects() and process_slab()
use DECLARE_BITMAP(map, page->objects);

With 65535 bits, we use 8192 bytes of stack ...

Switch these allocations to dynamic allocations.

Signed-off-by: Eric Dumazet <eric.dumazet(a)gmail.com>
Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>
---
mm/slub.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index b364844..7dc8e73 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2426,9 +2426,11 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
#ifdef CONFIG_SLUB_DEBUG
void *addr = page_address(page);
void *p;
- DECLARE_BITMAP(map, page->objects);
+ long *map = kzalloc(BITS_TO_LONGS(page->objects) * sizeof(long),
+ GFP_ATOMIC);

- bitmap_zero(map, page->objects);
+ if (!map)
+ return;
slab_err(s, page, "%s", text);
slab_lock(page);
for_each_free_object(p, s, page->freelist)
@@ -2443,6 +2445,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
}
}
slab_unlock(page);
+ kfree(map);
#endif
}

@@ -3648,10 +3651,10 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
}

static void process_slab(struct loc_track *t, struct kmem_cache *s,
- struct page *page, enum track_item alloc)
+ struct page *page, enum track_item alloc,
+ long *map)
{
void *addr = page_address(page);
- DECLARE_BITMAP(map, page->objects);
void *p;

bitmap_zero(map, page->objects);
@@ -3670,11 +3673,14 @@ static int list_locations(struct kmem_cache *s, char *buf,
unsigned long i;
struct loc_track t = { 0, 0, NULL };
int node;
+ unsigned long *map = kmalloc(BITS_TO_LONGS(oo_objects(s->max)) *
+ sizeof(unsigned long), GFP_KERNEL);

- if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
- GFP_TEMPORARY))
+ if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
+ GFP_TEMPORARY)) {
+ kfree(map);
return sprintf(buf, "Out of memory\n");
-
+ }
/* Push back cpu slabs */
flush_all(s);

@@ -3688,9 +3694,9 @@ static int list_locations(struct kmem_cache *s, char *buf,

spin_lock_irqsave(&n->list_lock, flags);
list_for_each_entry(page, &n->partial, lru)
- process_slab(&t, s, page, alloc);
+ process_slab(&t, s, page, alloc, map);
list_for_each_entry(page, &n->full, lru)
- process_slab(&t, s, page, alloc);
+ process_slab(&t, s, page, alloc, map);
spin_unlock_irqrestore(&n->list_lock, flags);
}

@@ -3741,6 +3747,7 @@ static int list_locations(struct kmem_cache *s, char *buf,
}

free_loc_track(&t);
+ kfree(map);
if (!t.count)
len += sprintf(buf, "No data\n");
return len;


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From: Christoph Lameter on 24 Mar 2010 17:30
Here is a patch for the second case. I think its better since it results
in an error display and it avoids the alloc for each slab. Add this piece
to your patch?

V1->V2 Fix missing kfree

Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>

---
mm/slub.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2010-03-24 16:23:19.000000000 -0500
+++ linux-2.6/mm/slub.c 2010-03-24 16:24:21.000000000 -0500
@@ -3648,10 +3648,10 @@ static int add_location(struct loc_track
}

static void process_slab(struct loc_track *t, struct kmem_cache *s,
- struct page *page, enum track_item alloc)
+ struct page *page, enum track_item alloc,
+ unsigned long *map)
{
void *addr = page_address(page);
- DECLARE_BITMAP(map, page->objects);
void *p;

bitmap_zero(map, page->objects);
@@ -3670,8 +3670,10 @@ static int list_locations(struct kmem_ca
unsigned long i;
struct loc_track t = { 0, 0, NULL };
int node;
+ unsigned long *map = kmalloc(BITS_TO_LONGS(oo_objects(s->max)) *
+ sizeof(unsigned long), GFP_KERNEL);

- if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
+ if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
GFP_TEMPORARY))
return sprintf(buf, "Out of memory\n");

@@ -3688,11 +3690,12 @@ static int list_locations(struct kmem_ca

spin_lock_irqsave(&n->list_lock, flags);
list_for_each_entry(page, &n->partial, lru)
- process_slab(&t, s, page, alloc);
+ process_slab(&t, s, page, alloc, map);
list_for_each_entry(page, &n->full, lru)
- process_slab(&t, s, page, alloc);
+ process_slab(&t, s, page, alloc, map);
spin_unlock_irqrestore(&n->list_lock, flags);
}
+ kfree(map);

for (i = 0; i < t.count; i++) {
struct location *l = &t.loc[i];
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From: Eric Dumazet on 24 Mar 2010 17:40
Le mercredi 24 mars 2010 à 16:25 -0500, Christoph Lameter a écrit :
> Here is a patch for the second case. I think its better since it results
> in an error display and it avoids the alloc for each slab. Add this piece
> to your patch?

Yes, I did it

>
> V1->V2 Fix missing kfree
>
> Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>
>
> ---
> mm/slub.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2010-03-24 16:23:19.000000000 -0500
> +++ linux-2.6/mm/slub.c 2010-03-24 16:24:21.000000000 -0500
> @@ -3648,10 +3648,10 @@ static int add_location(struct loc_track
> }
>
> static void process_slab(struct loc_track *t, struct kmem_cache *s,
> - struct page *page, enum track_item alloc)
> + struct page *page, enum track_item alloc,
> + unsigned long *map)
> {
> void *addr = page_address(page);
> - DECLARE_BITMAP(map, page->objects);
> void *p;
>
> bitmap_zero(map, page->objects);
> @@ -3670,8 +3670,10 @@ static int list_locations(struct kmem_ca
> unsigned long i;
> struct loc_track t = { 0, 0, NULL };
> int node;
> + unsigned long *map = kmalloc(BITS_TO_LONGS(oo_objects(s->max)) *
> + sizeof(unsigned long), GFP_KERNEL);
>
> - if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> + if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> GFP_TEMPORARY))

I also added a kfree(map); here

> return sprintf(buf, "Out of memory\n");
>
> @@ -3688,11 +3690,12 @@ static int list_locations(struct kmem_ca
>
> spin_lock_irqsave(&n->list_lock, flags);
> list_for_each_entry(page, &n->partial, lru)
> - process_slab(&t, s, page, alloc);
> + process_slab(&t, s, page, alloc, map);
> list_for_each_entry(page, &n->full, lru)
> - process_slab(&t, s, page, alloc);
> + process_slab(&t, s, page, alloc, map);
> spin_unlock_irqrestore(&n->list_lock, flags);
> }
> + kfree(map);
>
> for (i = 0; i < t.count; i++) {
> struct location *l = &t.loc[i];
> --



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From: Pekka Enberg on 25 Mar 2010 15:30
Eric Dumazet wrote:
> Le mercredi 24 mars 2010 à 16:14 -0500, Christoph Lameter a écrit :
>> Here is a patch for the second case. I think its better since it results
>> in an error display and it avoids the alloc for each slab. Add this piece
>> to your patch?
>>
>> Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>
>
> Sure, here is third version :

Christoph, does this look OK to you? I think Eric has all your later
additions and kfree() fixlets here.

> [PATCH] slub: Potential stack overflow
>
> I discovered that we can overflow stack if CONFIG_SLUB_DEBUG=y and use
> slabs with many objects, since list_slab_objects() and process_slab()
> use DECLARE_BITMAP(map, page->objects);
>
> With 65535 bits, we use 8192 bytes of stack ...
>
> Switch these allocations to dynamic allocations.
>
> Signed-off-by: Eric Dumazet <eric.dumazet(a)gmail.com>
> Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>
> ---
> mm/slub.c | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
> diff --git a/mm/slub.c b/mm/slub.c
> index b364844..7dc8e73 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2426,9 +2426,11 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
> #ifdef CONFIG_SLUB_DEBUG
> void *addr = page_address(page);
> void *p;
> - DECLARE_BITMAP(map, page->objects);
> + long *map = kzalloc(BITS_TO_LONGS(page->objects) * sizeof(long),
> + GFP_ATOMIC);
>
> - bitmap_zero(map, page->objects);
> + if (!map)
> + return;
> slab_err(s, page, "%s", text);
> slab_lock(page);
> for_each_free_object(p, s, page->freelist)
> @@ -2443,6 +2445,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
> }
> }
> slab_unlock(page);
> + kfree(map);
> #endif
> }
>
> @@ -3648,10 +3651,10 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
> }
>
> static void process_slab(struct loc_track *t, struct kmem_cache *s,
> - struct page *page, enum track_item alloc)
> + struct page *page, enum track_item alloc,
> + long *map)
> {
> void *addr = page_address(page);
> - DECLARE_BITMAP(map, page->objects);
> void *p;
>
> bitmap_zero(map, page->objects);
> @@ -3670,11 +3673,14 @@ static int list_locations(struct kmem_cache *s, char *buf,
> unsigned long i;
> struct loc_track t = { 0, 0, NULL };
> int node;
> + unsigned long *map = kmalloc(BITS_TO_LONGS(oo_objects(s->max)) *
> + sizeof(unsigned long), GFP_KERNEL);
>
> - if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> - GFP_TEMPORARY))
> + if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> + GFP_TEMPORARY)) {
> + kfree(map);
> return sprintf(buf, "Out of memory\n");
> -
> + }
> /* Push back cpu slabs */
> flush_all(s);
>
> @@ -3688,9 +3694,9 @@ static int list_locations(struct kmem_cache *s, char *buf,
>
> spin_lock_irqsave(&n->list_lock, flags);
> list_for_each_entry(page, &n->partial, lru)
> - process_slab(&t, s, page, alloc);
> + process_slab(&t, s, page, alloc, map);
> list_for_each_entry(page, &n->full, lru)
> - process_slab(&t, s, page, alloc);
> + process_slab(&t, s, page, alloc, map);
> spin_unlock_irqrestore(&n->list_lock, flags);
> }
>
> @@ -3741,6 +3747,7 @@ static int list_locations(struct kmem_cache *s, char *buf,
> }
>
> free_loc_track(&t);
> + kfree(map);
> if (!t.count)
> len += sprintf(buf, "No data\n");
> return len;
>
>

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From: Christoph Lameter on 25 Mar 2010 17:10
On Thu, 25 Mar 2010, Pekka Enberg wrote:

> Christoph, does this look OK to you? I think Eric has all your later additions
> and kfree() fixlets here.

Yes just dont know how to add an Ack given that there is already a
signoff.
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