linux-kernel - [PATCH v2 05/11] kcm: kcm_splice_read: always request MSG

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Message-ID: <0d8847df2f13e0831ee2f5504d06d5d12036d8f9.1703126594.git.nabijaczleweli@nabijaczleweli.xyz>
Date: Thu, 21 Dec 2023 04:09:03 +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>, 
	David Howells <dhowells@...hat.com>, Shigeru Yoshida <syoshida@...hat.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, Peilin Ye <peilin.ye@...edance.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 05/11] kcm: kcm_splice_read: always request MSG_DONTWAIT

Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time ‒ given:
	cat > kcm.c <<^D
	#define _GNU_SOURCE
	#include <fcntl.h>
	#include <sys/socket.h>
	#include <netinet/in.h>
	#include <linux/kcm.h>
	int main()
	{
		int kcm = socket(AF_KCM, SOCK_SEQPACKET, KCMPROTO_CONNECTED);
		for (;;)
			splice(kcm, 0, 1, 0, 128 * 1024 * 1024, 0);
	}
	^D
	cc kcm.c -o kcm
	mkfifo fifo
	./kcm > fifo &
	read -r _ < fifo &
	sleep 0.1
	echo zupa > fifo
kcm 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.

Also: don't pass the SPLICE_F_*-style flags argument to
skb_recv_datagram(), which expects MSG_*-style flags.
This fixes SPLICE_F_NONBLOCK not having worked.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@...ijaczleweli.xyz>
---
 net/kcm/kcmsock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 65d1f6755f98..ccfc46f31891 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1028,7 +1028,7 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos,
 
 	/* Only support splice for SOCKSEQPACKET */
 
-	skb = skb_recv_datagram(sk, flags, &err);
+	skb = skb_recv_datagram(sk, MSG_DONTWAIT, &err);
 	if (!skb)
 		goto err_out;
 
-- 
2.39.2

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