[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/ sweeper

[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/ sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N

Committed: https://crrev.com/779aa924f6d0066fe134ccbdc2abb9e5e15e100f
Cr-Commit-Position: refs/heads/master@{#33203}

[Michael Lippautz, 2016-01-11 09:24:41]

Description was changed from

==========
[heap] Ajust condition for AdjustLiveBytes to avoid concurrent access w/ sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N
==========

to

==========
[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/
sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N
==========

[Michael Lippautz, 2016-01-11 09:49:55]

mlippautz@chromium.org changed reviewers:
+ hpayer@chromium.org

[Michael Lippautz, 2016-01-11 09:49:56]

https://codereview.chromium.org/1576853002/diff/1/src/heap/mark-compact.cc
File src/heap/mark-compact.cc (right):

https://codereview.chromium.org/1576853002/diff/1/src/heap/mark-compact.cc#ne...
src/heap/mark-compact.cc:3985: sweeping_in_progress_ = true;
This is not really needed as we sweep on the main thread (thus cannot have any
concurrent access with the markbits).

However, for correctness (of sweeping_in_progress()) we should indicate that we
are already sweeping?

[Hannes Payer (out of office), 2016-01-11 12:28:41]

lgtm

https://codereview.chromium.org/1576853002/diff/1/src/heap/mark-compact.cc
File src/heap/mark-compact.cc (right):

https://codereview.chromium.org/1576853002/diff/1/src/heap/mark-compact.cc#ne...
src/heap/mark-compact.cc:3985: sweeping_in_progress_ = true;
On 2016/01/11 09:49:56, Michael Lippautz wrote:
> This is not really needed as we sweep on the main thread (thus cannot have any
> concurrent access with the markbits).
> 
> However, for correctness (of sweeping_in_progress()) we should indicate that
we
> are already sweeping?

Acknowledged.

[Michael Lippautz, 2016-01-11 12:36:08]

The CQ bit was checked by mlippautz@chromium.org

[commit-bot: I haz the power, 2016-01-11 12:36:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1576853002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1576853002/1

[commit-bot: I haz the power, 2016-01-11 12:58:06]

Description was changed from

==========
[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/
sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N
==========

to

==========
[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/
sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N
==========

[commit-bot: I haz the power, 2016-01-11 12:58:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-01-11 12:59:07]

Description was changed from

==========
[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/
sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N
==========

to

==========
[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/
sweeper

A concurrent sweeper thread can access the same markbit cell as the main thread
during right trimming a fixed array, resulting in a data race on a markbit cell.
Previously we checked whether we were currently marking incrementally, filtering
out this case.

The current check has the benefit of keeping live_bytes accurate (modulo other
bugs) until the sweeper starts.

BUG=chromium:576193
LOG=N

Committed: https://crrev.com/779aa924f6d0066fe134ccbdc2abb9e5e15e100f
Cr-Commit-Position: refs/heads/master@{#33203}
==========

[commit-bot: I haz the power, 2016-01-11 12:59:10]

Patchset 1 (id:??) landed as
https://crrev.com/779aa924f6d0066fe134ccbdc2abb9e5e15e100f
Cr-Commit-Position: refs/heads/master@{#33203}