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

Anton Vorontsov
2009-04-30T14:12:33Z

On Thu, Apr 30, 2009 at 03:05:42PM +0200, Nick Piggin wrote:
[...]
> ---
> 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;

Cosmetic issue: spaces instead of tabs are used on these
three lines.

> + 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 {

--
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2