code review 11324044: cmd/gc: do not race instrument syscall.forkAndExecInChild

cmd/gc: do not race instrument syscall.forkAndExecInChild
Race instrumentation can allocate, switch stacks, preempt, etc.
All that is not allowed in between fork and exec.
Fixes issue 4840.

[dvyukov, 2013-07-16 09:43:26]

Hello golang-dev@googlegroups.com,

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

[DMorsing, 2013-07-16 10:51:34]

LGTM.

[dave_cheney.net, 2013-07-16 10:58:30]

LGTM. Thank you very much for working on this.

https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_bsd.go
File src/pkg/syscall/exec_bsd.go (right):

https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_bsd.go...
src/pkg/syscall/exec_bsd.go:30: // For the same reason compiler does not race
instrument it.
For the same reason the compiler does instrument concurrent calls to this
function.

https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_linux.go
File src/pkg/syscall/exec_linux.go (right):

https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_linux....
src/pkg/syscall/exec_linux.go:31: // For the same reason compiler does not race
instrument it.
same

[dvyukov, 2013-07-16 11:27:22]

https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_bsd.go
File src/pkg/syscall/exec_bsd.go (right):

https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_bsd.go...
src/pkg/syscall/exec_bsd.go:30: // For the same reason compiler does not race
instrument it.
On 2013/07/16 10:58:30, dfc wrote:
> For the same reason the compiler does instrument concurrent calls to this
> function.

I do not understand this.
With this change the compiler does NOT instrument this functions.
I do not see how concurrent calls come into picture.

[dave_cheney.net, 2013-07-16 11:32:53]

This was my mistake, please ignore my comment.

On Tue, Jul 16, 2013 at 9:27 PM,  <dvyukov@google.com> wrote:
>
> https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_bsd.go
> File src/pkg/syscall/exec_bsd.go (right):
>
>
https://codereview.appspot.com/11324044/diff/6001/src/pkg/syscall/exec_bsd.go...
> src/pkg/syscall/exec_bsd.go:30: // For the same reason compiler does not
> race instrument it.
> On 2013/07/16 10:58:30, dfc wrote:
>>
>> For the same reason the compiler does instrument concurrent calls to
>
> this
>>
>> function.
>
>
> I do not understand this.
> With this change the compiler does NOT instrument this functions.
> I do not see how concurrent calls come into picture.
>
> https://codereview.appspot.com/11324044/

[dvyukov, 2013-07-16 11:35:19]

*** Submitted as https://code.google.com/p/go/source/detail?r=9f9fdf917ffc ***

cmd/gc: do not race instrument syscall.forkAndExecInChild
Race instrumentation can allocate, switch stacks, preempt, etc.
All that is not allowed in between fork and exec.
Fixes issue 4840.

R=golang-dev, daniel.morsing, dave
CC=golang-dev
https://codereview.appspot.com/11324044

[rsc, 2013-07-16 13:22:53]

LGTM