netdev - [PATCH next] iov_iter: fix copy_page_from_iter

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Date: Fri, 6 Oct 2023 21:32:59 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: David Howells <dhowells@...hat.com>
cc: Christian Brauner <brauner@...nel.org>, Jens Axboe <axboe@...nel.dk>, 
    Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>, 
    Christian Brauner <christian@...uner.io>, 
    David Laight <David.Laight@...lab.com>, 
    Matthew Wilcox <willy@...radead.org>, Jeff Layton <jlayton@...nel.org>, 
    linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org, 
    linux-mm@...ck.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH next] iov_iter: fix copy_page_from_iter_atomic()

[PATCH next] iov_iter: fix copy_page_from_iter_atomic()

Trying to test tmpfs on latest linux-next, copying and building kernel
trees, huge pages, and swapping while swapping off involved: lots of
cp: error writing '/tmp/2624/Documentation/fb/vesafb.txt': Bad address
cp: error writing '/tmp/2624/arch/mips/math-emu/dp_fsp.c': Bad address
etc.

Bisection leads to next-20231006's 376fdc4552f1 ("iov_iter:
Don't deal with iter->copy_mc in memcpy_from_iter_mc()") from vfs.git.
The tweak below makes it healthy again: please feel free to fold in.

Signed-off-by: Hugh Dickins <hughd@...gle.com>

--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -497,7 +497,7 @@ size_t copy_page_from_iter_atomic(struct
 		}

 		p = kmap_atomic(page) + offset;
-		__copy_from_iter(p, n, i);
+		n = __copy_from_iter(p, n, i);
 		kunmap_atomic(p);
 		copied += n;
 		offset += n;