From d6d7170de414c16a7ea0125b5a458272557227b6 Mon Sep 17 00:00:00 2001 From: Dmitriy Vyukov Date: Fri, 8 Aug 2014 20:13:57 +0400 Subject: [PATCH] runtime: fix data race in stackalloc 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 --- src/pkg/runtime/stack.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/pkg/runtime/stack.c b/src/pkg/runtime/stack.c index 0a806e8fab..772080af55 100644 --- a/src/pkg/runtime/stack.c +++ b/src/pkg/runtime/stack.c @@ -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);