iomap: Fix error handling in iomap_zero_iter()

iomap_write_end() does not return a negative errno to indicate an
error, but the number of bytes successfully copied.  It cannot return
an error today, so include a debugging assertion like the one in
iomap_unshare_iter().

Fixes: c6f40468657d ("fsdax: decouple zeroing from the iomap buffered I/O code")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211221044450.517558-1-willy@infradead.org
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index ac040d607f4feb8610ce05a2603840e4069549f2..49279dfa73c9b199d3e575a6519241a680078bf1 100644 (file)
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -895,8 +895,8 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
                mark_page_accessed(page);
 
                bytes = iomap_write_end(iter, pos, bytes, bytes, page);
-               if (bytes < 0)
-                       return bytes;
+               if (WARN_ON_ONCE(bytes == 0))
+                       return -EIO;
 
                pos += bytes;
                length -= bytes;