linux-kernel - Re: iov_iter

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Message-ID: <20170428182511.GM29622@ZenIV.linux.org.uk>
Date:   Fri, 28 Apr 2017 19:25:12 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dave Jones <davej@...emonkey.org.uk>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: iov_iter_pipe warning.

On Fri, Apr 28, 2017 at 06:20:25PM +0100, Al Viro wrote:
> On Fri, Apr 28, 2017 at 12:50:24PM -0400, Dave Jones wrote:
> > currently running v4.11-rc8-75-gf83246089ca0
> > 
> > sunrpc bit is for the other unrelated problem I'm chasing.
> > 
> > note also, I saw the backtrace without the fs/splice.c changes.
> 
> 	Interesting...  Could you add this and see if that triggers?

Gyah...  It's a bloody dumb braino in iov_iter_revert() for pipe-backed
ones.  Sorry, the oneliner below should fix it.

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f7c93568ec99..4952311422c1 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -798,7 +798,7 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
 		while (1) {
 			size_t n = off - pipe->bufs[idx].offset;
 			if (unroll < n) {
-				off -= (n - unroll);
+				off -= unroll;
 				break;
 			}
 			unroll -= n;