On Tue 05-06-12 15:56:01, Andrew Morton wrote:
> 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 ;)
Yup ;)
> 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)) {
Ah, nice trick :) Thanks.
> /*
> * 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.
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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