os/exec: skip poll descriptors when checking for open descriptors

It turns out that there is a path that initializes netpoll and opens
file descriptors before running the os/exec init function: on some
systems, the uses of NewFile when setting os.Stdin and friends can
initialize netpoll which can open file descriptors. This in itself
is not a problem, but when we check whether the new files are open
using os.NewFile, a side-effect is to put them into non-blocking mode.
This can then break future uses of netpoll.

Updates #35469
Fixes #35566

Change-Id: I1b2e2c943695d1c2d29496b050abbce9ee710a00
Reviewed-on: https://go-review.googlesource.com/c/go/+/207078
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
index 0498c7d9150bb79b994f8cfafade75db43341a1c..19bda6902a94d1d360ee0d8ff182a4d5fa514758 100644 (file)
--- a/src/os/exec/exec_test.go
+++ b/src/os/exec/exec_test.go
@@ -47,6 +47,9 @@ func init() {
                return
        }
        for fd := uintptr(3); fd <= 100; fd++ {
+               if poll.IsPollDescriptor(fd) {
+                       continue
+               }
                // We have no good portable way to check whether an FD is open.
                // We use NewFile to create a *os.File, which lets us
                // know whether it is open, but then we have to cope with