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runtime: fix data race in stackalloc

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Stack shrinking happens during mark phase,
and it assumes that it owns stackcache in mcache.
Stack cache flushing also happens during mark phase,
and it accesses stackcache's w/o any synchronization.
This leads to stackcache corruption:
http://goperfd.appspot.com/log/309af5571dfd7e1817259b9c9cf9bcf9b2c27610

LGTM=khr
R=khr
CC=golang-codereviews, rsc
https://golang.org/cl/126870043
This commit is contained in:
Dmitriy Vyukov 2014-08-08 20:13:57 +04:00
parent a83bbc9c48
commit d6d7170de4
1 changed files with 5 additions and 3 deletions
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8
src/pkg/runtime/stack.c
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@ -223,9 +223,11 @@ runtime·stackalloc(G *gp, uint32 n)
n2 >>= 1;
}
c = g->m->mcache;
if(c == nil) {
// This can happen in the guts of exitsyscall or
if(c == nil || g->m->gcing || g->m->helpgc) {
// c == nil can happen in the guts of exitsyscall or
// procresize. Just get a stack from the global pool.
// Also don't touch stackcache during gc
// as it's flushed concurrently.
runtime·lock(&stackpoolmu);
x = poolalloc(order);
runtime·unlock(&stackpoolmu);
@ -285,7 +287,7 @@ runtime·stackfree(G *gp, void *v, Stktop *top)
}
x = (MLink*)v;
c = g->m->mcache;
if(c == nil) {
if(c == nil || g->m->gcing || g->m->helpgc) {
runtime·lock(&stackpoolmu);
poolfree(x, order);
runtime·unlock(&stackpoolmu);