[v2,07/11] net/tcp: tcp_splice_read: always do non-blocking reads
Commit Message
Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time ‒ given:
cat > tcp.c <<^D
#define _GNU_SOURCE
#include <fcntl.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <linux/tls.h>
int main()
{
int s = socket(AF_INET, SOCK_STREAM, 0);
struct sockaddr_in addr = {
.sin_family = AF_INET,
.sin_addr = { htonl(INADDR_LOOPBACK) },
.sin_port = htons(getpid() % (0xFFFF - 1000) + 1000)
};
bind(s, &addr, sizeof(addr));
listen(s, 1);
if (!fork()) {
connect(socket(AF_INET, SOCK_STREAM, 0), &addr, sizeof(addr));
sleep(100);
return 0;
}
s = accept(s, NULL, NULL);
for (;;)
splice(s, 0, 1, 0, 128 * 1024 * 1024, 0);
}
^D
cc tcp.c -o tcp
mkfifo fifo
./tcp > fifo &
read -r _ < fifo &
sleep 0.1
echo zupa > fifo
tcp 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.
sock_rcvtimeo() returns 0 if the second argument is true, so the
explicit re-try loop for empty read conditions can be removed
entirely.
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
---
net/ipv4/tcp.c | 32 +++-----------------------------
1 file changed, 3 insertions(+), 29 deletions(-)
@@ -782,7 +782,6 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
.len = len,
.flags = flags,
};
- long timeo;
ssize_t spliced;
int ret;
@@ -797,7 +796,6 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
lock_sock(sk);
- timeo = sock_rcvtimeo(sk, sock->file->f_flags & O_NONBLOCK);
while (tss.len) {
ret = __tcp_splice_read(sk, &tss);
if (ret < 0)
@@ -821,37 +819,13 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
ret = -ENOTCONN;
break;
}
- if (!timeo) {
- ret = -EAGAIN;
- break;
- }
- /* if __tcp_splice_read() got nothing while we have
- * an skb in receive queue, we do not want to loop.
- * This might happen with URG data.
- */
- if (!skb_queue_empty(&sk->sk_receive_queue))
- break;
- ret = sk_wait_data(sk, &timeo, NULL);
- if (ret < 0)
- break;
- if (signal_pending(current)) {
- ret = sock_intr_errno(timeo);
- break;
- }
- continue;
+ ret = -EAGAIN;
+ break;
}
tss.len -= ret;
spliced += ret;
- if (!tss.len || !timeo)
- break;
- release_sock(sk);
- lock_sock(sk);
-
- if (sk->sk_err || sk->sk_state == TCP_CLOSE ||
- (sk->sk_shutdown & RCV_SHUTDOWN) ||
- signal_pending(current))
- break;
+ break;
}
release_sock(sk);