runtime: see whether gp==nil before checking preemption state

Recent we changed from using gFromTLS to using gFromSP, which apparently sometimes returns nil. This causes crashes when dereferenced. Fix that by not checking for preemption in the case that gFromSP returns nil. Fixes golang#44679. Change-Id: I0199ebe7cd113379c5fa35c27932d913df79092a Reviewed-on: https://go-review.googlesource.com/c/go/+/297390 Trust: Jason A. Donenfeld <[email protected]> Run-TryBot: Jason A. Donenfeld <[email protected]> TryBot-Result: Go Bot <[email protected]> Reviewed-by: Russ Cox <[email protected]>
catap · Apr 8, 2021 · 98dd205 · 98dd205
1 parent 46ffbec
commit 98dd205
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
@@ -1380,7 +1380,7 @@ func preemptM(mp *m) {
 
 	// Does it want a preemption and is it safe to preempt?
 	gp := gFromSP(mp, c.sp())
-	if wantAsyncPreempt(gp) {
+	if gp != nil && wantAsyncPreempt(gp) {
 		if ok, newpc := isAsyncSafePoint(gp, c.ip(), c.sp(), c.lr()); ok {
 			// Inject call to asyncPreempt
 			targetPC := funcPC(asyncPreempt)