linux-kernel - [PATCH v2 01/11] splice: copy_splice_read: do the I/O with IOCB

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Message-ID: <d87ac02081f2d698dde10da7da51336afc59b480.1703126594.git.nabijaczleweli@nabijaczleweli.xyz>
Date: Thu, 21 Dec 2023 04:08:45 +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, linux-kernel@...r.kernel.org
Subject: [PATCH v2 01/11] splice: copy_splice_read: do the I/O with
 IOCB_NOWAIT

Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time ‒ given:
	cat > udp.c <<^D
	#define _GNU_SOURCE
	#include <fcntl.h>
	#include <sys/socket.h>
	#include <netinet/in.h>
	#include <netinet/udp.h>
	int main()
	{
		int s = socket(AF_INET, SOCK_DGRAM, 0);
		bind(s,
		     &(struct sockaddr_in){ .sin_family = AF_INET,
					    .sin_addr.s_addr = htonl(INADDR_ANY) },
		     sizeof(struct sockaddr_in));
		for (;;)
			splice(s, 0, 1, 0, 128 * 1024 * 1024, 0);
	}
	^D
	cc udp.c -o udp
	mkfifo fifo
	./udp > fifo &
	read -r _ < fifo &
	sleep 0.1
	echo zupa > fifo
udp 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>
---
 fs/splice.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/splice.c b/fs/splice.c
index d983d375ff11..9d29664f23ee 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -361,6 +361,7 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
 	iov_iter_bvec(&to, ITER_DEST, bv, npages, len);
 	init_sync_kiocb(&kiocb, in);
 	kiocb.ki_pos = *ppos;
+	kiocb.ki_flags |= IOCB_NOWAIT;
 	ret = call_read_iter(in, &kiocb, &to);
 
 	if (ret > 0) {
-- 
2.39.2

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