runtime: don't crash on mlock failure

Instead, note that mlock has failed, start trying the mitigation of
touching the signal stack before sending a preemption signal, and,
if the program crashes, mention the possible problem and a wiki page
describing the issue (https://golang.org/wiki/LinuxKernelSignalVectorBug).

Tested on a kernel in the buggy version range, but with the patch,
by using `ulimit -l 0`.

Fixes #37436

Change-Id: I072aadb2101496dffd655e442fa5c367dad46ce8
Reviewed-on: https://go-review.googlesource.com/c/go/+/223121
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/runtime/os_linux.go b/src/runtime/os_linux.go
index e0e3f4e341..d8c1827852 100644
--- a/src/runtime/os_linux.go
+++ b/src/runtime/os_linux.go
@@ -5,6 +5,7 @@
 package runtime
 
 import (
+	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
 )
@@ -479,7 +480,21 @@ func rt_sigaction(sig uintptr, new, old *sigactiont, size uintptr) int32
 func getpid() int
 func tgkill(tgid, tid, sig int)
 
+// touchStackBeforeSignal stores an errno value. If non-zero, it means
+// that we should touch the signal stack before sending a signal.
+// This is used on systems that have a bug when the signal stack must
+// be faulted in.  See #35777 and #37436.
+//
+// This is accessed atomically as it is set and read in different threads.
+//
+// TODO(austin): Remove this after Go 1.15 when we remove the
+// mlockGsignal workaround.
+var touchStackBeforeSignal uint32
+
 // signalM sends a signal to mp.
 func signalM(mp *m, sig int) {
+	if atomic.Load(&touchStackBeforeSignal) != 0 {
+		atomic.Cas((*uint32)(unsafe.Pointer(mp.gsignal.stack.hi-4)), 0, 0)
+	}
 	tgkill(getpid(), int(mp.procid), sig)
 }