netdev - [PATCH v2 02/11] af_unix: unix_stream_splice_read: always request MSG

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Date: Thu, 21 Dec 2023 04:08:51 +0100
From: 
	Ahelenia Ziemiańska <nabijaczleweli@...ijaczleweli.xyz>
Cc: Jens Axboe <axboe@...nel.dk>, Christian Brauner <brauner@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, David Howells <dhowells@...hat.com>, 
	Alexander Mikhalitsyn <alexander@...alicyn.com>, John Fastabend <john.fastabend@...il.com>, 
	Daan De Meyer <daan.j.demeyer@...il.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 02/11] af_unix: unix_stream_splice_read: always request
 MSG_DONTWAIT

Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time ‒ given:
	cat > unix.c <<^D
	#define _GNU_SOURCE
	#include <fcntl.h>
	#include <sys/socket.h>
	#include <sys/un.h>
	int main()
	{
		int sp[2];
		socketpair(AF_UNIX, SOCK_STREAM, 0, sp);
		for (;;)
			splice(sp[0], 0, 1, 0, 128 * 1024 * 1024, 0);
	}
	^D
	cc unix.c -o unix
	mkfifo fifo
	./unix > fifo &
	read -r _ < fifo &
	sleep 0.1
	echo zupa > fifo
unix used to sleep in splice and the shell used to enter an
uninterruptible sleep in open("fifo");
now the splice returns -EAGAIN and the whole program completes.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@...ijaczleweli.xyz>
---
 net/unix/af_unix.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ac1f2bc18fc9..bae84552bf58 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2921,15 +2921,12 @@ static ssize_t unix_stream_splice_read(struct socket *sock,  loff_t *ppos,
 		.pipe = pipe,
 		.size = size,
 		.splice_flags = flags,
+		.flags = MSG_DONTWAIT,
 	};
 
 	if (unlikely(*ppos))
 		return -ESPIPE;
 
-	if (sock->file->f_flags & O_NONBLOCK ||
-	    flags & SPLICE_F_NONBLOCK)
-		state.flags = MSG_DONTWAIT;
-
 	return unix_stream_read_generic(&state, false);
 }
 
-- 
2.39.2

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