Revert "os: make FindProcess use pidfd on Linux"

This reverts CL 542699.

Reason for revert: Some applications assume FindProcess does not return
errors.

For #62654.
Fixes #65866.

Change-Id: Ic185a6253c8e508b08150b618c39a9905f6cdd60
Reviewed-on: https://go-review.googlesource.com/c/go/+/566476
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>

1 files changed, 1 insertions, 8 deletions

diff --git a/src/os/exec.go b/src/os/exec.go
index 7ef1fee595..42e8a399a9 100644
--- a/src/os/exec.go
+++ b/src/os/exec.go
@@ -86,17 +86,10 @@ func Getppid() int { return syscall.Getppid() }
 // The Process it returns can be used to obtain information
 // about the underlying operating system process.
 //
-// On Unix systems other than Linux, FindProcess always succeeds and returns a Process
+// On Unix systems, FindProcess always succeeds and returns a Process
 // for the given pid, regardless of whether the process exists. To test whether
 // the process actually exists, see whether p.Signal(syscall.Signal(0)) reports
 // an error.
-//
-// On Linux, FindProcess may either return ErrProcessGone for a non-existing
-// process (thus eliminating the need to use a signal to check if the process
-// exists), or work the same way as for other Unix systems, described above,
-// depending on the kernel version used and the system configuration. The old
-// behavior (of always succeeding) can be enforced by using GODEBUG setting
-// osfinderr=0.
 func FindProcess(pid int) (*Process, error) {
 	return findProcess(pid)
 }