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runtime: don't lock mheap on user goroutine

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This is bad for 2 reasons:
1. if the code under lock ever grows stack,
it will deadlock as stack growing acquires mheap lock.
2. It currently deadlocks with SetCPUProfileRate:
scavenger locks mheap, receives prof signal and tries to lock prof lock;
meanwhile SetCPUProfileRate locks prof lock and tries to grow stack
(presumably in runtime.unlock->futexwakeup). Boom.
Let's assume that it
Fixes #8407.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews, khr
https://golang.org/cl/112640043
This commit is contained in:
Dmitriy Vyukov 2014-07-23 18:52:25 +04:00
parent 0603fbb01c
commit e91704af27
1 changed files with 2 additions and 6 deletions
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8
src/pkg/runtime/mheap.c
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@ -642,7 +642,6 @@ static FuncVal forcegchelperv = {(void(*)(void))forcegchelper};
void
runtime·MHeap_Scavenger(void)
{
MHeap *h;
uint64 tick, forcegc, limit;
int64 unixnow;
int32 k;
@ -662,15 +661,12 @@ runtime·MHeap_Scavenger(void)
else
tick = limit/2;
h = &runtime·mheap;
for(k=0;; k++) {
runtime·noteclear(&note);
runtime·notetsleepg(&note, tick);
runtime·lock(h);
unixnow = runtime·unixnanotime();
if(unixnow - mstats.last_gc > forcegc) {
runtime·unlock(h);
// The scavenger can not block other goroutines,
// otherwise deadlock detector can fire spuriously.
// GC blocks other goroutines via the runtime·worldsema.
@ -680,13 +676,13 @@ runtime·MHeap_Scavenger(void)
runtime·notetsleepg(&note, -1);
if(runtime·debug.gctrace > 0)
runtime·printf("scvg%d: GC forced\n", k);
runtime·lock(h);
}
runtime·unlock(h);
g->m->locks++; // ensure that we are on the same m while filling arguments
g->m->scalararg[0] = k;
g->m->scalararg[1] = runtime·nanotime();
g->m->scalararg[2] = limit;
runtime·mcall(scavenge_m);
g->m->locks--;
}
}