nfs: can_coalesce_requests must enforce contiguity

Commit c725a143c853ce524f32458032dbabc0616419f2
"nfs: allow coalescing of subpage requests" got rid of the requirement
that requests cover whole pages, but it made some incorrect assumptions.

It turns out that callers of this interface can map adjacent requests
(by file position as seen by req_offset + req->wb_bytes) to different pages,
even when they could share a page. An example is the direct I/O interface -
iov_iter_get_pages_alloc may return one segment with a partial page filled
and the next segment (which is adjacent in the file position) starts with a
new page.

Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index a1d1de7b97c5fdeb6e7665c81c091db8eefaad65..932c6cc27a7664a29c9bf8d5883990c510e59b02 100644 (file)
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -823,6 +823,14 @@ static bool nfs_can_coalesce_requests(struct nfs_page *prev,
                        return false;
                if (req_offset(req) != req_offset(prev) + prev->wb_bytes)
                        return false;
+               if (req->wb_page == prev->wb_page) {
+                       if (req->wb_pgbase != prev->wb_pgbase + prev->wb_bytes)
+                               return false;
+               } else {
+                       if (req->wb_pgbase != 0 ||
+                           prev->wb_pgbase + prev->wb_bytes != PAGE_CACHE_SIZE)
+                               return false;
+               }
        }
        size = pgio->pg_ops->pg_test(pgio, prev, req);
        WARN_ON_ONCE(size > req->wb_bytes);