tcp_splice: Don't handle EPOLL_CTL_DEL as part of tcp_splice_epoll_ctl()

tcp_splice_epoll_ctl() removes both sockets from the epoll set if called
when conn->flags & CLOSING.  This will always happen immediately after
setting that flag, since conn_flag_do() makes the call itself.  That's also
the _only_ time it can happen: we perform the EPOLL_CTL_DEL without
clearing the conn->in_epoll flag, meaning that any further calls to
tcp_splice_epoll_ctl() would attempt EPOLL_CTL_MOD, which would necessarily
fail since the fds are no longer in the epoll.

The EPOLL_CTL_DEL path in tcp_splice_epoll_ctl() has essentially zero
overlap with anything else the function does, so just move them to be
open coded in conn_flag_do().

This does require kernel 2.6.9 or later, in order to pass NULL as the
event structure for epoll_ctl().  However, we already require at least
3.13 to allow unprivileged user namespaces.

Given that, simply directly perform the EPOLL_CTL_DEL operations from
conn_flag_do() rather than unnecessarily multiplexini

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 4 insertions, 8 deletions

diff --git a/tcp_splice.c b/tcp_splice.c
index 6c4c664..570a8c6 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -152,8 +152,10 @@ static void conn_flag_do(const struct ctx *c, struct tcp_splice_conn *conn,
 		}
 	}
 
-	if (flag == CLOSING)
-		tcp_splice_epoll_ctl(c, conn);
+	if (flag == CLOSING) {
+		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, conn->a, NULL);
+		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, conn->b, NULL);
+	}
 }
 
 #define conn_flag(c, conn, flag)					\
@@ -182,12 +184,6 @@ static int tcp_splice_epoll_ctl(const struct ctx *c,
 	struct epoll_event ev_b = { .data.u64 = ref_b.u64 };
 	uint32_t events_a, events_b;
 
-	if (conn->flags & CLOSING) {
-		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, conn->a, &ev_a);
-		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, conn->b, &ev_b);
-		return 0;
-	}
-
 	tcp_splice_conn_epoll_events(conn->events, &events_a, &events_b);
 	ev_a.events = events_a;
 	ev_b.events = events_b;