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runtime: fix GC bitmap corruption

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Fixes #8299.

R=golang-codereviews
CC=golang-codereviews, khr, rsc
https://golang.org/cl/103640044
This commit is contained in:
Dmitriy Vyukov 2014-06-28 19:20:46 -07:00
parent 94935cb5c1
commit 5bfe8adee5
1 changed files with 13 additions and 2 deletions
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15
src/pkg/runtime/mgc0.c
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@ -2731,7 +2731,7 @@ runtime·markscan(void *v)
void
runtime·markfreed(void *v)
{
uintptr *b, off, shift;
uintptr *b, off, shift, xbits;
if(0)
runtime·printf("markfreed %p\n", v);
@ -2742,7 +2742,18 @@ runtime·markfreed(void *v)
off = (uintptr*)v - (uintptr*)runtime·mheap.arena_start; // word offset
b = (uintptr*)runtime·mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
*b = (*b & ~(bitMask<<shift)) | (bitAllocated<<shift);
if(!g->m->gcing || work.nproc == 1) {
// During normal operation (not GC), the span bitmap is not updated concurrently,
// because either the span is cached or accesses are protected with MCentral lock.
*b = (*b & ~(bitMask<<shift)) | (bitAllocated<<shift);
} else {
// During GC other threads concurrently mark heap.
for(;;) {
xbits = *b;
if(runtime·casp((void**)b, (void*)xbits, (void*)((xbits & ~(bitMask<<shift)) | (bitAllocated<<shift))))
break;
}
}
}
// check that the block at v of size n is marked freed.