tree d4bdfbcac7d82bcef4f16f2e7e661320a5ebc6dc
parent bba5c1887a925a9945d22217d38d58d8b3ba1043
author Weston Andros Adamson <dros@primarydata.com> 1408052373 -0400
committer Trond Myklebust <trond.myklebust@primarydata.com> 1408745084 -0400

nfs: can_coalesce_requests must enforce contiguity

Commit 6094f83864c1d1296566a282cba05ba613f151ee
"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>