internal/poll, runtime: handle netpollopen error in poll_runtime_poll…

…Open

When netpollopen in poll_runtime_pollOpen returns an error, the work in
runtime_pollUnblock and runtime_pollClose can be avoided since the
underlying system call to set up the poller failed.

E.g. on linux, this avoids calling netpollclose and thus epoll_ctl(fd,
EPOLL_CTL_DEL, ...) in case the file does not support epoll, i.e.
epoll_ctl(fd, EPOLL_CTL_ADD, ...) in netpollopen failed.

Fixes #44552

Change-Id: I564d90340fd1ab3a6490526353616a447ae0cfb8
Reviewed-on: https://go-review.googlesource.com/c/go/+/297392
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/internal/poll/fd_poll_runtime.go

@@ -39,10 +39,6 @@ func (pd *pollDesc) init(fd *FD) error {
 	serverInit.Do(runtime_pollServerInit)
 	ctx, errno := runtime_pollOpen(uintptr(fd.Sysfd))
 	if errno != 0 {
-		if ctx != 0 {
-			runtime_pollUnblock(ctx)
-			runtime_pollClose(ctx)
-		}
 		return errnoErr(syscall.Errno(errno))
 	}
 	pd.runtimeCtx = ctx

src/runtime/netpoll.go

@@ -162,9 +162,12 @@ func poll_runtime_pollOpen(fd uintptr) (*pollDesc, int) {
 	pd.self = pd
 	unlock(&pd.lock)
 
-	var errno int32
-	errno = netpollopen(fd, pd)
-	return pd, int(errno)
+	errno := netpollopen(fd, pd)
+	if errno != 0 {
+		pollcache.free(pd)
+		return nil, int(errno)
+	}
+	return pd, 0
 }
 
 //go:linkname poll_runtime_pollClose internal/poll.runtime_pollClose