runtime: always run stackalloc on scheduler stack
Avoids deadlocks like the one below, in which a stack split happened
in order to call lock(&stacks), but then the stack unsplit cannot run
because stacks is now locked.
The only code calling stackalloc that wasn't on a scheduler
stack already was malg, which creates a new goroutine.
runtime.futex+0x23 /home/rsc/g/go/src/pkg/runtime/linux/amd64/sys.s:139
runtime.futex()
futexsleep+0x50 /home/rsc/g/go/src/pkg/runtime/linux/thread.c:51
futexsleep(0x5b0188, 0x300000003, 0x100020000, 0x4159e2)
futexlock+0x85 /home/rsc/g/go/src/pkg/runtime/linux/thread.c:119
futexlock(0x5b0188, 0x5b0188)
runtime.lock+0x56 /home/rsc/g/go/src/pkg/runtime/linux/thread.c:158
runtime.lock(0x5b0188, 0x7f0d27b4a000)
runtime.stackfree+0x4d /home/rsc/g/go/src/pkg/runtime/malloc.goc:336
runtime.stackfree(0x7f0d27b4a000, 0x1000, 0x8, 0x7fff37e1e218)
runtime.oldstack+0xa6 /home/rsc/g/go/src/pkg/runtime/proc.c:705
runtime.oldstack()
runtime.lessstack+0x22 /home/rsc/g/go/src/pkg/runtime/amd64/asm.s:224
runtime.lessstack()
----- lessstack called from goroutine 2 -----
runtime.lock+0x56 /home/rsc/g/go/src/pkg/runtime/linux/thread.c:158
runtime.lock(0x5b0188, 0x40a5e2)
runtime.stackalloc+0x55 /home/rsc/g/go/src/pkg/runtime/malloc.c:316
runtime.stackalloc(0x1000, 0x4055b0)
runtime.malg+0x3d /home/rsc/g/go/src/pkg/runtime/proc.c:803
runtime.malg(0x1000, 0x40add9)
runtime.newproc1+0x12b /home/rsc/g/go/src/pkg/runtime/proc.c:854
runtime.newproc1(0xf840027440, 0x7f0d27b49230, 0x0, 0x49f238, 0x40, ...)
runtime.newproc+0x2f /home/rsc/g/go/src/pkg/runtime/proc.c:831
runtime.newproc(0x0, 0xf840027440, 0xf800000010, 0x44b059)
...
R=r, r2
CC=golang-dev
https://golang.org/cl/4216045
diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index abbf63b..4106068 100644
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -394,6 +394,12 @@
{
void *v;
+ // Stackalloc must be called on scheduler stack, so that we
+ // never try to grow the stack during the code that stackalloc runs.
+ // Doing so would cause a deadlock (issue 1547).
+ if(g != m->g0)
+ runtime·throw("stackalloc not on scheduler stack");
+
if(m->mallocing || m->gcing || n == FixedStack) {
runtime·lock(&stacks);
if(stacks.size == 0)
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index c471fff..1d38258 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -380,6 +380,7 @@
break;
case Grunning:
case Grecovery:
+ case Gstackalloc:
if(gp != g)
runtime·throw("mark - world not stopped");
scanstack(gp);
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 1bbca63..455a39e 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -253,8 +253,10 @@
}
// Mark runnable.
- if(g->status == Grunnable || g->status == Grunning || g->status == Grecovery)
+ if(g->status == Grunnable || g->status == Grunning || g->status == Grecovery || g->status == Gstackalloc) {
+ runtime·printf("goroutine %d has status %d\n", g->goid, g->status);
runtime·throw("bad g->status in ready");
+ }
g->status = Grunnable;
gput(g);
@@ -492,6 +494,13 @@
runtime·free(d);
runtime·gogo(&gp->sched, 1);
}
+
+ if(gp->status == Gstackalloc) {
+ // switched to scheduler stack to call stackalloc.
+ gp->param = runtime·stackalloc((uintptr)gp->param);
+ gp->status = Grunning;
+ runtime·gogo(&gp->sched, 1);
+ }
// Jumped here via runtime·gosave/gogo, so didn't
// execute lock(&runtime·sched) above.
@@ -509,6 +518,8 @@
switch(gp->status){
case Grunnable:
case Gdead:
+ case Grecovery:
+ case Gstackalloc:
// Shouldn't have been running!
runtime·throw("bad gp->status in sched");
case Grunning:
@@ -795,18 +806,35 @@
G*
runtime·malg(int32 stacksize)
{
- G *g;
+ G *newg;
byte *stk;
+ int32 oldstatus;
- g = runtime·malloc(sizeof(G));
+ newg = runtime·malloc(sizeof(G));
if(stacksize >= 0) {
- stk = runtime·stackalloc(StackSystem + stacksize);
- g->stack0 = stk;
- g->stackguard = stk + StackSystem + StackGuard;
- g->stackbase = stk + StackSystem + stacksize - sizeof(Stktop);
- runtime·memclr(g->stackbase, sizeof(Stktop));
+ if(g == m->g0) {
+ // running on scheduler stack already.
+ stk = runtime·stackalloc(StackSystem + stacksize);
+ } else {
+ // have to call stackalloc on scheduler stack.
+ oldstatus = g->status;
+ g->param = (void*)(StackSystem + stacksize);
+ g->status = Gstackalloc;
+ // next two lines are runtime·gosched without the check
+ // of m->locks. we're almost certainly holding a lock,
+ // but this is not a real rescheduling so it's okay.
+ if(runtime·gosave(&g->sched) == 0)
+ runtime·gogo(&m->sched, 1);
+ stk = g->param;
+ g->param = nil;
+ g->status = oldstatus;
+ }
+ newg->stack0 = stk;
+ newg->stackguard = stk + StackSystem + StackGuard;
+ newg->stackbase = stk + StackSystem + stacksize - sizeof(Stktop);
+ runtime·memclr(newg->stackbase, sizeof(Stktop));
}
- return g;
+ return newg;
}
/*
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index ac992a2..4456e9b 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -104,6 +104,7 @@
Gmoribund,
Gdead,
Grecovery,
+ Gstackalloc,
};
enum
{
