netdev - Re: [PATCH] pipe_to_sendpage: Ensure that MSG_MORE is set if we set MSG_SENDPAGE

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Date:	Sun, 24 Nov 2013 17:25:06 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	viro@...iv.linux.org.uk, shawnlandden@...il.com,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au, Tom Herbert <therbert@...gle.com>,
	"David S. Miller" <davem@...emloft.net>, stable@...r.kernel.org
Subject: Re: [PATCH] pipe_to_sendpage: Ensure that MSG_MORE is set if we set
 MSG_SENDPAGE_NOTLAST

On Mon, 2013-11-25 at 00:42 +0100, Richard Weinberger wrote:
> Commit 35f9c09fe (tcp: tcp_sendpages() should call tcp_push() once)
> added an internal flag MSG_SENDPAGE_NOTLAST.
> We have to ensure that MSG_MORE is also set if we set MSG_SENDPAGE_NOTLAST.
> Otherwise users that check against MSG_MORE will not see it.
> 
> This fixes sendfile() on AF_ALG.
> 
> Cc: Tom Herbert <therbert@...gle.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: <stable@...r.kernel.org> # 3.4.x
> Reported-and-tested-by: Shawn Landden <shawnlandden@...il.com>
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
>  fs/splice.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 3b7ee65..b93f1b8 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -701,7 +701,7 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
>  	more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
>  
>  	if (sd->len < sd->total_len && pipe->nrbufs > 1)
> -		more |= MSG_SENDPAGE_NOTLAST;
> +		more |= MSG_SENDPAGE_NOTLAST | MSG_MORE;
>  
>  	return file->f_op->sendpage(file, buf->page, buf->offset,
>  				    sd->len, &pos, more);

I do not think this patch is right. It looks like a revert of a useful
patch for TCP zero copy. Given the time it took to discover this
regression, I bet tcp zero copy has more users than AF_ALG, by 5 or 6
order of magnitude ;)

Here we want to make the difference between the two flags, not merge
them.

If AF_ALG do not care of the difference, try instead :

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index ef5356cd280a..850246206b12 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -114,6 +114,9 @@ static ssize_t hash_sendpage(struct socket *sock, struct page *page,
 	struct hash_ctx *ctx = ask->private;
 	int err;
 
+	if (flags & MSG_SENDPAGE_NOTLAST)
+		flags |= MSG_MORE;
+
 	lock_sock(sk);
 	sg_init_table(ctx->sgl.sg, 1);
 	sg_set_page(ctx->sgl.sg, page, size, offset);



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