Re: [PATCH 3/6] lib/scatterlist: Do not leak pages when high-order allocation fails

[Tvrtko Ursulin]

On 07/03/18 16:16, Bart Van Assche wrote:
> On Wed, 2018-03-07 at 12:47 +0000, Tvrtko Ursulin wrote:
> > diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> > index 9884be50a2c0..e13a759c5c49 100644
> > --- a/lib/scatterlist.c
> > +++ b/lib/scatterlist.c
> > @@ -493,7 +493,7 @@ struct scatterlist *sgl_alloc_order(unsigned long length, unsigned int order,
> >   {
> >   	unsigned int chunk_len = PAGE_SIZE << order;
> >   	struct scatterlist *sgl, *sg;
> > -	unsigned int nent;
> > +	unsigned int nent, i;
> >   
> >   	nent = round_up(length, chunk_len) >> (PAGE_SHIFT + order);
> >   
> > @@ -517,11 +517,12 @@ struct scatterlist *sgl_alloc_order(unsigned long length, unsigned int order,
> >   
> >   	sg_init_table(sgl, nent);
> >   	sg = sgl;
> > +	i = 0;
> >   	while (length) {
> >   		struct page *page = alloc_pages(gfp, order);
> >   
> >   		if (!page) {
> > -			sgl_free(sgl);
> > +			sgl_free_n_order(sgl, i, order);
> >   			return NULL;
> >   		}
> >   
> > @@ -529,6 +530,7 @@ struct scatterlist *sgl_alloc_order(unsigned long length, unsigned int order,
> >   		sg_set_page(sg, page, chunk_len, 0);
> >   		length -= chunk_len;
> >   		sg = sg_next(sg);
> > +		i++;
> >   	}
>
> Since the entire sg-list is zero-initialized before this loop starts, since
> the sg-list is not chained onto another sg-list before this function returns
> and since sgl_free_n_order() checks whether or not each page pointer is NULL
> before freeing it I think we don't need the new loop variable 'i' and that
> we can call sgl_free_order() instead of sgl_free_n_order().

Yes true, I've only realized that in a later patch. Can rebase to move 
that change earlier in.

Regards,

Tvrtko