code review 91010048: runtime: do not set m->locks around memory allocation

runtime: do not set m->locks around memory allocation
If slice append is the only place where a program allocates,
then it will consume all available memory w/o triggering GC.
This was demonstrated in the issue.
Fixes issue 7922.

[dvyukov, 2014-05-02 11:14:21]

Hello golang-codereviews@googlegroups.com (cc: iant@golang.org, khr@golang.org,
rsc@golang.org),

I'd like you to review this change to
https://dvyukov%40google.com@code.google.com/p/go/

[rsc, 2014-05-02 16:15:44]

Why is this safe? Why does the comment no longer apply?

[dvyukov, 2014-05-02 16:21:39]

On 2014/05/02 16:15:44, rsc wrote:
> Why is this safe? Why does the comment no longer apply?

The old comment says:
// Here we allocate with FlagNoZero but potentially w/o FlagNoScan,	
// GC must not see this blocks until memclr below.

With this change we use either both FlagNoScan|FlagNoZero or none of them. We
don't use FlagNoZero w/o FlagNoScan (dangerous combination), so the old comment
does not apply.

[rsc, 2014-05-02 16:33:38]

LGTM

[dvyukov, 2014-05-02 16:39:31]

*** Submitted as https://code.google.com/p/go/source/detail?r=afef4a014b0e ***

runtime: do not set m->locks around memory allocation
If slice append is the only place where a program allocates,
then it will consume all available memory w/o triggering GC.
This was demonstrated in the issue.
Fixes issue 7922.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews, iant, khr
https://codereview.appspot.com/91010048