Commit 5887f142 authored by Dmitriy Vyukov's avatar Dmitriy Vyukov Committed by Russ Cox

runtime: more reliable preemption

Currently preemption signal g->stackguard0==StackPreempt
can be lost if it is received when preemption is disabled
(e.g. m->lock!=0). This change duplicates the preemption
signal in g->preempt and restores g->stackguard0
when preemption is enabled.
Update #543.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/10792043
parent a8374859
......@@ -5,6 +5,7 @@
// +build freebsd linux
#include "runtime.h"
#include "stack.h"
// This implementation depends on OS-specific implementations of
//
......@@ -99,6 +100,8 @@ runtime·unlock(Lock *l)
if(--m->locks < 0)
runtime·throw("runtime·unlock: lock count");
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
// One-time notifications.
......
......@@ -5,6 +5,7 @@
// +build darwin netbsd openbsd plan9 windows
#include "runtime.h"
#include "stack.h"
// This implementation depends on OS-specific implementations of
//
......@@ -112,6 +113,8 @@ runtime·unlock(Lock *l)
if(--m->locks < 0)
runtime·throw("runtime·unlock: lock count");
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
// One-time notifications.
......
......@@ -13,6 +13,7 @@ package runtime
#include "type.h"
#include "typekind.h"
#include "race.h"
#include "stack.h"
MHeap runtime·mheap;
......@@ -94,6 +95,8 @@ runtime·mallocgc(uintptr size, uint32 flag, int32 dogc, int32 zeroed)
*(uintptr*)((uintptr)v+size-sizeof(uintptr)) = 0;
m->mallocing = 0;
if(g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
if(!(flag & FlagNoProfiling) && (rate = runtime·MemProfileRate) > 0) {
if(size >= rate)
......
......@@ -2014,6 +2014,7 @@ runtime·gc(int32 force)
}
// all done
m->gcing = 0;
runtime·semrelease(&runtime·worldsema);
runtime·starttheworld();
......@@ -2031,6 +2032,8 @@ runtime·gc(int32 force)
// give the queued finalizers, if any, a chance to run
runtime·gosched();
}
if(g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
static void
......@@ -2115,7 +2118,6 @@ gc(struct gc_args *args)
cachestats();
mstats.next_gc = mstats.heap_alloc+mstats.heap_alloc*gcpercent/100;
m->gcing = 0;
t4 = runtime·nanotime();
mstats.last_gc = t4;
......
......@@ -294,6 +294,8 @@ runtime·ready(G *gp)
if(runtime·atomicload(&runtime·sched.npidle) != 0 && runtime·atomicload(&runtime·sched.nmspinning) == 0) // TODO: fast atomic
wakep();
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
int32
......@@ -475,6 +477,8 @@ runtime·starttheworld(void)
newm(mhelpgc, nil);
}
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
// Called to start an M.
......@@ -564,6 +568,8 @@ runtime·allocm(P *p)
if(p == m->p)
releasep();
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
return mp;
}
......@@ -1008,6 +1014,7 @@ execute(G *gp)
runtime·throw("execute: bad g status");
}
gp->status = Grunning;
gp->preempt = false;
gp->stackguard0 = gp->stackguard;
m->p->tick++;
m->curg = gp;
......@@ -1433,6 +1440,8 @@ runtime·exitsyscall(void)
// so okay to clear gcstack and gcsp.
g->gcstack = (uintptr)nil;
g->gcsp = (uintptr)nil;
if(g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
return;
}
......@@ -1450,6 +1459,8 @@ runtime·exitsyscall(void)
g->status = Grunning;
g->gcstack = (uintptr)nil;
g->gcsp = (uintptr)nil;
if(g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
return;
}
}
......@@ -1620,6 +1631,8 @@ runtime·newproc1(FuncVal *fn, byte *argp, int32 narg, int32 nret, void *callerp
if(runtime·atomicload(&runtime·sched.npidle) != 0 && runtime·atomicload(&runtime·sched.nmspinning) == 0 && fn->fn != runtime·main) // TODO: fast atomic
wakep();
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
return newg;
}
......@@ -2174,6 +2187,7 @@ if(1) return;
gp = mp->curg;
if(gp == nil || gp == mp->g0)
return;
gp->preempt = true;
gp->stackguard0 = StackPreempt;
}
......
......@@ -253,6 +253,7 @@ struct G
bool issystem; // do not output in stack dump
bool isbackground; // ignore in deadlock detector
bool blockingsyscall; // hint that the next syscall will block
bool preempt; // preemption signal, duplicates stackguard0 = StackPreempt
int8 raceignore; // ignore race detection events
M* m; // for debuggers, but offset not hard-coded
M* lockedm;
......
......@@ -250,7 +250,7 @@ runtime·newstack(void)
// We are interested in preempting user Go code, not runtime code.
if(oldstatus != Grunning || m->locks || m->mallocing || m->gcing) {
// Let the goroutine keep running for now.
// TODO(dvyukov): remember but delay the preemption.
// gp->preempt is set, so it will be preempted next time.
gp->stackguard0 = gp->stackguard;
gp->status = oldstatus;
runtime·gogo(&gp->sched); // never return
......
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