From f2f2434d47c711dcbe7d3abdee4293ae0f4c0739 Mon Sep 17 00:00:00 2001 From: Richard Miller Date: Thu, 17 Mar 2016 10:20:54 +0000 Subject: [PATCH] syscall: avoid failure in plan9 StartProcess from fd close race Between the enumeration of fdsToClose in the parent and the closing of fds in the child, it's possible for a file to be closed in another thread. If that file descriptor is reused when opening the child-parent status pipe, it will be closed prematurely in the child and the forkExec gets out of sync. This has been observed to cause failures in builder tests when the link step of a build is started before the compile step has run, with "file does not exist" messages as the visible symptom. The simple workaround is to check against closing the pipe. A more comprehensive solution would be to rewrite the fd closing code to avoid races, along the lines of the long ago proposed https://golang.org/cl/57890043 - but meanwhile this correction will prevent some builder failures. Change-Id: I4ef5eaea70c21d00f4df0e0847a1c5b2966de7da Reviewed-on: https://go-review.googlesource.com/20800 Run-TryBot: David du Colombier <0intro@gmail.com> Reviewed-by: David du Colombier <0intro@gmail.com> --- src/syscall/exec_plan9.go | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/src/syscall/exec_plan9.go b/src/syscall/exec_plan9.go index b9e78c5ab4..28a746580b 100644 --- a/src/syscall/exec_plan9.go +++ b/src/syscall/exec_plan9.go @@ -219,7 +219,9 @@ func forkAndExecInChild(argv0 *byte, argv []*byte, envv []envItem, dir *byte, at // Close fds we don't need. for i = 0; i < len(fdsToClose); i++ { - RawSyscall(SYS_CLOSE, uintptr(fdsToClose[i]), 0, 0) + if fdsToClose[i] != pipe { + RawSyscall(SYS_CLOSE, uintptr(fdsToClose[i]), 0, 0) + } } if envv != nil { -- 2.48.1