On Wed, 6 Jun 2012 00:40:56 +0200
Jan Kara <jack@xxxxxxx> wrote:
> If someone calls vb_alloc() (or vm_map_ram() for that matter) to allocate
> 0 bytes (0 pages), get_order() returns BITS_PER_LONG - PAGE_CACHE_SHIFT
> and interesting stuff happens. So make debugging such problems easier and
> warn about 0-size allocation.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> mm/vmalloc.c | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 2aad499..bebee70 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -904,6 +904,15 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
>
> BUG_ON(size & ~PAGE_MASK);
> BUG_ON(size > PAGE_SIZE*VMAP_MAX_ALLOC);
> + if (size == 0) {
> + /*
> + * Allocating 0 bytes isn't what caller wants since
> + * get_order(0) returns funny result. Just warn and terminate
> + * early.
> + */
> + WARN_ON(1);
> + return NULL;
> + }
> order = get_order(size);
Spose so. You got bitten, I assume ;)
We can neaten the implementation:
--- a/mm/vmalloc.c~mm-make-vb_alloc-more-foolproof-fix
+++ a/mm/vmalloc.c
@@ -904,13 +904,12 @@ static void *vb_alloc(unsigned long size
BUG_ON(size & ~PAGE_MASK);
BUG_ON(size > PAGE_SIZE*VMAP_MAX_ALLOC);
- if (size == 0) {
+ if (WARN_ON(size == 0)) {
/*
* Allocating 0 bytes isn't what caller wants since
* get_order(0) returns funny result. Just warn and terminate
* early.
*/
- WARN_ON(1);
return NULL;
}
order = get_order(size);
and that gives us the unlikely() hit too.
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