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runtime: fix transient _Gwaiting states in newstack

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With concurrent stack shrinking, the stack can move the instant after
a G enters _Gwaiting. There are only two places that put a G into
_Gwaiting: gopark and newstack. We fixed uses of gopark. This commit
fixes newstack by simplifying its G transitions and, in particular,
eliminating or narrowing the transient _Gwaiting states it passes
through so it's clear nothing in the G is accessed while in _Gwaiting.

For #12967.

Change-Id: I2440ead411d2bc61beb1e2ab020ebe3cb3481af9
Reviewed-on: https://go-review.googlesource.com/20039
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Austin Clements 2016-02-25 15:37:40 -05:00
parent 8fb182d020
commit 3c2a21ff13
1 changed files with 5 additions and 6 deletions
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11
src/runtime/stack.go
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@ -869,11 +869,6 @@ func newstack() {
}
}
// The goroutine must be executing in order to call newstack,
// so it must be Grunning (or Gscanrunning).
casgstatus(gp, _Grunning, _Gwaiting)
gp.waitreason = "stack growth"
if gp.stack.lo == 0 {
throw("missing stack in newstack")
}
@ -908,6 +903,8 @@ func newstack() {
if thisg.m.p == 0 && thisg.m.locks == 0 {
throw("runtime: g is running but p is not")
}
// Synchronize with scang.
casgstatus(gp, _Grunning, _Gwaiting)
if gp.preemptscan {
for !castogscanstatus(gp, _Gwaiting, _Gscanwaiting) {
// Likely to be racing with the GC as
@ -941,7 +938,9 @@ func newstack() {
throw("stack overflow")
}
casgstatus(gp, _Gwaiting, _Gcopystack)
// The goroutine must be executing in order to call newstack,
// so it must be Grunning (or Gscanrunning).
casgstatus(gp, _Grunning, _Gcopystack)
// The concurrent GC will not scan the stack while we are doing the copy since
// the gp is in a Gcopystack status.