Re: [PATCH rdma-next v4 2/3] lib/scatterlist: Fix wrong update of orig_nents

From: Maor Gottlieb
Date: Wed Aug 25 2021 - 00:59:54 EST



On 8/24/2021 10:12 PM, Jason Gunthorpe wrote:
On Tue, Aug 24, 2021 at 05:25:30PM +0300, Maor Gottlieb wrote:
@@ -514,11 +531,13 @@ struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
offset = 0;
cur_page = j;
}
- sgt->nents += added_nents;
+ sgt_append->sgt.nents += added_nents;
+ sgt_append->sgt.orig_nents = sgt_append->sgt.nents;
+ sgt_append->prv = s;
Why is nents being touched here?

Shouldn't it just be

sgt_append->sgt.orig_nents += added_nents;
sgt_append->prv = s;

?

In general yes, but all the sg_alloc_* functions update both orig_nents and nents (to same value). May be drivers that pass nents instead of orig_nents to dma_map_sg* (like umem did before this patch set). So I prefer to set it here as well, also not to break sg_alloc_table_from_pages_segment which use the same path. This kind of change could be done very carefully next cycle for all sg_alloc_*.


Let me know I can fix it

Jason