[PATCH v2 05/11] kcm: kcm_splice_read: always request MSG_DONTWAIT

["Ahelenia Ziemiańska" <nabijaczleweli@nabijaczleweli.xyz>]

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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@nabijaczleweli.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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