On Fri, Jul 29, 2022 at 11:12:45PM +0200, Alexander Gordeev wrote:
> On Fri, Jul 29, 2022 at 06:21:23PM +0100, Al Viro wrote:
> > > Hi Al,
> > >
> > > This changes causes sendfile09 LTP testcase fail in linux-next
> > > (up to next-20220727) on s390. In fact, not this change exactly,
> > > but rather 92d4d18eecb9 ("new iov_iter flavour - ITER_UBUF") -
> > > which differs from what is posted here.
> > >
> > > AFAICT page_cache_pipe_buf_confirm() encounters !PageUptodate()
> > > and !page->mapping page and returns -ENODATA.
> > >
> > > I am going to narrow the testcase and get more details, but please
> > > let me know if I am missing something.
> >
> > Grrr....
> >
> > - } else if (iter_is_iovec(to)) {
> > + } else if (!user_backed_iter(to)) {
> >
> > in mm/shmem.c. Spot the typo...
> >
> > Could you check if replacing that line with
> > } else if (user_backed_iter(to)) {
> >
> > fixes the breakage?
>
> Yes, it does! So just to be sure - this is the fix:
FWIW, there'd been another braino, caught by test from Hugh Dickins;
this one in ITER_PIPE: allocate buffers as we go in copy-to-pipe primitives
Incremental follows; folded and pushed out.
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 642841ce7595..939078ffbfb5 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -469,7 +469,7 @@ static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
struct page *page = append_pipe(i, n, &off);
chunk = min_t(size_t, n, PAGE_SIZE - off);
if (!page)
- break;
+ return bytes - n;
memcpy_to_page(page, off, addr, chunk);
addr += chunk;
}
@@ -774,7 +774,7 @@ static size_t pipe_zero(size_t bytes, struct iov_iter *i)
char *p;
if (!page)
- break;
+ return bytes - n;
chunk = min_t(size_t, n, PAGE_SIZE - off);
p = kmap_local_page(page);
memset(p + off, 0, chunk);
diff --git a/mm/shmem.c b/mm/shmem.c
index 6b83f3971795..6c8a84a1fbbb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2603,7 +2603,7 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
ret = copy_page_to_iter(page, offset, nr, to);
put_page(page);
- } else if (!user_backed_iter(to)) {
+ } else if (user_backed_iter(to)) {
/*
* Copy to user tends to be so well optimized, but
* clear_user() not so much, that it is noticeably
