Re: Next April 28: boot failure on PowerPC with SLQB

Nick Piggin
2009-04-30T13:06:26Z

On Thu, Apr 30, 2009 at 02:20:29PM +0300, Pekka Enberg wrote:
> On Thu, 2009-04-30 at 13:18 +0200, Nick Piggin wrote:
> > OK thanks. So I think we have 2 problems. One with MAX_ORDER <= 9
> > that is fixed by the previous patch, and another which is probably
> > due to having no memory on node 0 which I will take another look
> > at now.
> >
> > We can merge the previous patch now, though.
>
> Hmm, I'll bet this BUG_ON triggers for Stephen.
>
> diff --git a/mm/slqb.c b/mm/slqb.c
> index a651843..e4b3859 100644
> --- a/mm/slqb.c
> +++ b/mm/slqb.c
> @@ -1391,6 +1391,7 @@ static noinline void *__slab_alloc_page(struct kmem_cache *s,
> struct kmem_cache_node *n;
>
> n = s->node_slab[slqb_page_to_nid(page)];
> + BUG_ON(!n);
> l = &n->list;
> page->list = l;

Hmm, this might do it. The following code now passes some stress testing
in a userspace harness wheras before it did not (and was obviously wrong).

---
SLQB: fix dumb early allocation cache

The dumb early allocation cache had a bug where it could allow allocation
to go past the end of a page, which could cause crashes or random memory
corruption. Fix this and simplify the logic.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
mm/slqb.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

Index: linux-2.6/mm/slqb.c
===================================================================
--- linux-2.6.orig/mm/slqb.c
+++ linux-2.6/mm/slqb.c
@@ -2185,8 +2185,11 @@ static void *kmem_cache_dyn_array_alloc(
{
size_t size = sizeof(void *) * ids;

+ BUG_ON(!size);
+
if (unlikely(!slab_is_available())) {
static void *nextmem;
+ static size_t nextleft;
void *ret;

/*
@@ -2194,16 +2197,16 @@ static void *kmem_cache_dyn_array_alloc(
* never get freed by definition so we can do it rather
* simply.
*/
- if (!nextmem) {
- nextmem = alloc_pages_exact(size, GFP_KERNEL);
- if (!nextmem)
- return NULL;
+ if (size > nextleft) {
+ nextmem = alloc_pages_exact(size, GFP_KERNEL);
+ if (!nextmem)
+ return NULL;
+ nextleft = roundup(size, PAGE_SIZE);
}
+
ret = nextmem;
- nextmem = (void *)((unsigned long)ret + size);
- if ((unsigned long)ret >> PAGE_SHIFT !=
- (unsigned long)nextmem >> PAGE_SHIFT)
- nextmem = NULL;
+ nextleft -= size;
+ nextmem += size;
memset(ret, 0, size);
return ret;
} else {