linux-kernel - Re: iov_iter

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Message-ID: <20170428172024.GL29622@ZenIV.linux.org.uk>
Date:   Fri, 28 Apr 2017 18:20:25 +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 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?

diff --git a/fs/splice.c b/fs/splice.c
index 540c4a44756c..12a12d9c313f 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -306,6 +306,9 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
 	kiocb.ki_pos = *ppos;
 	ret = call_read_iter(in, &kiocb, &to);
 	if (ret > 0) {
+		if (WARN_ON(iov_iter_count(&to) != len - ret))
+			printk(KERN_ERR "ops %p: was %zd, left %zd, returned %d\n",
+				in->f_op, len, iov_iter_count(&to), ret);
 		*ppos = kiocb.ki_pos;
 		file_accessed(in);
 	} else if (ret < 0) {