1406119 - Unable to scroll on about:preferences

Status: VERIFIED FIXED

(Core :: Graphics: WebRender, defect, P1)

Description

[Kartikaya Gupta (email:[e-mail])]

Spinoff from https://bugzilla.mozilla.org/show_bug.cgi?id=1406008#c5:

Jan Andre Ikenmeyer [:darkspirit] from bug 1406008 comment 5:
> layers force accel + webrender
> 
> "bad" is when I am not able to scroll down on about:preferences when
> webrender is enabled.
> 
> > mozregression --good 2017-10-03 --bad 2017-10-05 --profile-persistence clone-first
> > [...]
> > 6:09.50 INFO: Last good revision: 29a20bc04c6f95f8014238511d2cce7f299fabf3about:preferences
> > 6:09.50 INFO: First bad revision: 6869bf44878df743ee848048954a959f77d5d9d7
> > 6:09.50 INFO: Pushlog:
> > https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=29a20bc04c6f95f8014238511d2cce7f299fabf3&tochange=6869bf44878df743ee848048954a959f77d5d9d7
> 
> Bug 1404782 - Do not mutate display list in layers-free mode. r=mattwoodrow

My investigation:

Kartikaya Gupta (email:[e-mail]) from bug 1406008 comment 6:
> It looks like the patch adds a recursive call at [1] which is not handled
> properly. The code assumes that only recursion that can happen is at [2] and
> does a whole bunch of stuff beforehand (e.g. recording stuff like
> layerCountBeforeRecursing and all the things inside the apzEnabled block)
> and that's not happening around this new recursive call site. That's going
> to result in the event regions being all messed up which could very well
> explain the bad scrolling.
> 
> [1] https://hg.mozilla.org/integration/autoland/rev/db40593b664c#l1.58 
> [2]
> http://searchfox.org/mozilla-central/rev/
> 7ba03cebf1dcf3b4c40c85a4efad42a5022cf1ec/gfx/layers/wr/WebRenderLayerManager.
> cpp#333-335

Comment 1

[Kartikaya Gupta (email:[e-mail])]

Attachment: Bug 1406119 - Ensure that we do all the necessary APZ prep before recursing.

Bug 1404782 added another codepath that allows the CreateWebRenderCommandsFromDisplayList
function to recurse. However recursion is tricky when APZ is enabled because
we need to do a bunch of setup and teardown to properly build event regions and
track APZ state. This patch moves the new recursion codepath inside the setup
and teardown, so that it works as intended.

Review commit: https://reviewboard.mozilla.org/r/186882/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/186882/

Comment 2

[Kartikaya Gupta (email:[e-mail])]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=9bb4c9876cf88df698755af22bfb406e06890e70

Comment 3

[Ethan Lin[:ethlin]]

Comment on attachment 8915683 [details]
Bug 1406119 - Ensure that we do all the necessary APZ prep before recursing.

https://reviewboard.mozilla.org/r/186882/#review192070

Thanks. I followed the FLB's way to process the display list, but I didn't think of this.

Comment 4

[Kartikaya Gupta (email:[e-mail])]

No worries, the code is really convoluted and I hope to delete it soon ;)

Comment 5

[Mozilla Autoland]

hg error in cmd: hg pull upstream: pulling from https://hg.mozilla.org/integration/autoland
searching for changes
abort: HTTP Error 500: Internal Server Error

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/eaaaba7a4a80
Ensure that we do all the necessary APZ prep before recursing. r=ethlin

Comment 7

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/eaaaba7a4a80

Comment 8

[Darkspirit]

Verified fixed in Nightly 58 x64 20171008131700 @ Debian Testing.
Thank you!