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runtime: fix concurrent GC sweep

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The issue was that one of the MSpan_Sweep callers
was doing sweep with preemption enabled.
Additional checks are added.

LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://golang.org/cl/62990043
This commit is contained in:
Dmitriy Vyukov 2014-02-13 19:36:45 +04:00
parent 9c767b64ee
commit f8e4a2ef94
1 changed files with 24 additions and 8 deletions
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32
src/pkg/runtime/mgc0.c
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@ -66,7 +66,7 @@ enum {
CollectStats = 0,
ScanStackByFrames = 1,
IgnorePreciseGC = 0,
ConcurrentSweep = 0,
ConcurrentSweep = 1,
// Four bits per word (see #defines below).
wordsPerBitmapWord = sizeof(void*)*8/4,
@ -1694,10 +1694,13 @@ runtime·MSpan_EnsureSwept(MSpan *s)
sg = runtime·mheap.sweepgen;
if(runtime·atomicload(&s->sweepgen) == sg)
return;
m->locks++;
if(runtime·cas(&s->sweepgen, sg-2, sg-1)) {
runtime·MSpan_Sweep(s);
m->locks--;
return;
}
m->locks--;
// unfortunate condition, and we don't have efficient means to wait
while(runtime·atomicload(&s->sweepgen) != sg)
runtime·osyield();
@ -1709,13 +1712,13 @@ runtime·MSpan_EnsureSwept(MSpan *s)
bool
runtime·MSpan_Sweep(MSpan *s)
{
int32 cl, n, npages;
int32 cl, n, npages, nfree;
uintptr size, off, *bitp, shift, bits;
uint32 sweepgen;
byte *p;
MCache *c;
byte *arena_start;
MLink head, *end;
int32 nfree;
byte *type_data;
byte compression;
uintptr type_data_inc;
@ -1723,9 +1726,14 @@ runtime·MSpan_Sweep(MSpan *s)
Special *special, **specialp, *y;
bool res, sweepgenset;
if(s->state != MSpanInUse || s->sweepgen != runtime·mheap.sweepgen-1) {
// It's critical that we enter this function with preemption disabled,
// GC must not start while we are in the middle of this function.
if(m->locks == 0 && m->mallocing == 0 && g != m->g0)
runtime·throw("MSpan_Sweep: m is not locked");
sweepgen = runtime·mheap.sweepgen;
if(s->state != MSpanInUse || s->sweepgen != sweepgen-1) {
runtime·printf("MSpan_Sweep: state=%d sweepgen=%d mheap.sweepgen=%d\n",
s->state, s->sweepgen, runtime·mheap.sweepgen);
s->state, s->sweepgen, sweepgen);
runtime·throw("MSpan_Sweep: bad span state");
}
arena_start = runtime·mheap.arena_start;
@ -1820,7 +1828,7 @@ runtime·MSpan_Sweep(MSpan *s)
runtime·unmarkspan(p, 1<<PageShift);
*(uintptr*)p = (uintptr)0xdeaddeaddeaddeadll; // needs zeroing
// important to set sweepgen before returning it to heap
runtime·atomicstore(&s->sweepgen, runtime·mheap.sweepgen);
runtime·atomicstore(&s->sweepgen, sweepgen);
sweepgenset = true;
if(runtime·debug.efence)
runtime·SysFree(p, size, &mstats.gc_sys);
@ -1851,8 +1859,16 @@ runtime·MSpan_Sweep(MSpan *s)
}
}
if(!sweepgenset)
runtime·atomicstore(&s->sweepgen, runtime·mheap.sweepgen);
if(!sweepgenset) {
// The span must be in our exclusive ownership until we update sweepgen,
// check for potential races.
if(s->state != MSpanInUse || s->sweepgen != sweepgen-1) {
runtime·printf("MSpan_Sweep: state=%d sweepgen=%d mheap.sweepgen=%d\n",
s->state, s->sweepgen, sweepgen);
runtime·throw("MSpan_Sweep: bad span state after sweep");
}
runtime·atomicstore(&s->sweepgen, sweepgen);
}
if(nfree) {
c->local_nsmallfree[cl] += nfree;
c->local_cachealloc -= nfree * size;