runtime: call throw on systemstack in exitsyscall

If exitsyscall tries to grow the stack it will panic, but throw calls
print, which can grow the stack. Move the two bare throws in
exitsyscall to the system stack.

Updates #21431.

Change-Id: I5b29da5d34ade908af648a12075ed327a864476c
Reviewed-on: https://go-review.googlesource.com/79517
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 0492a4139ddbad660fdb448d99c2c5daea7c4c1f..8cb6e57a9702d09138e21b04733d1c48bf76a309 100644 (file)
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2939,7 +2939,9 @@ func exitsyscall(dummy int32) {
        oldp := _g_.m.p.ptr()
        if exitsyscallfast() {
                if _g_.m.mcache == nil {
-                       throw("lost mcache")
+                       systemstack(func() {
+                               throw("lost mcache")
+                       })
                }
                if trace.enabled {
                        if oldp != _g_.m.p.ptr() || _g_.m.syscalltick != _g_.m.p.ptr().syscalltick {
@@ -2986,7 +2988,9 @@ func exitsyscall(dummy int32) {
        mcall(exitsyscall0)
 
        if _g_.m.mcache == nil {
-               throw("lost mcache")
+               systemstack(func() {
+                       throw("lost mcache")
+               })
        }
 
        // Scheduler returned, so we're allowed to run now.