1460697 - MOZ_PROFILER_SHUTDOWN crash in ExtensionPolicyService from locked_profiler_stream_json_for_this_process

Status: RESOLVED FIXED

(Core :: Gecko Profiler, defect, P2)

Description

[Benoit Girard (:BenWa)]

Attachment: backtrace

Backtrace attached.

STR is:
$ MOZ_PROFILER_STARTUP=true MOZ_PROFILER_SHUTDOWN=file.sps /Applications/Firefox\ Nightly.app/Contents/MacOS/firefox

This is easier to setup automation because right now WebDriver can't call nsIProfiler.

Comment 1

[Panos Astithas (he/him) [:past] (please ni?)]

This is an assertion in:

https://searchfox.org/mozilla-central/rev/babf96cf0c37b608e9663e2af73a4d21819c4af1/toolkit/components/extensions/ExtensionPolicyService.cpp#80

ExtensionPolicyService::ExtensionPolicyService()
{
  mObs = services::GetObserverService();
  MOZ_RELEASE_ASSERT(mObs);

Kris, since you wrote this code, do you have any ideas on what is the right fix here?

Comment 2

[Kris Maglione [:kmag]]

It looks like the profiler is trying to collect metadata very late in the process shutdown cycle. At that point, the cached policy service singleton has been cleared, and XPCOM has been shutdown, so it can't initialize a new one.

That's a bit worrisome, really. It seems like the profiler shouldn't be trying to collect metadata that late, since it will be, at most, incomplete and possibly inaccurate.

But I guess to solve the immediate problem, we could just check whether XPCOM shutdown has already started, and skip gathering extension metadata if it has.

Comment 3

[Nazım Can Altınova [:canova][:canaltinova on phabricator]]

Attachment: Bug 1460697 - Do not collect extension metadata for profiler while XPCOM is shutting down

To collect extension metadata, we need to get an ExtensionPolicyService singleton,
but during shutdown, we are deleting the ExtensionPolicyService instance and then
trying to collect extension metadata. Since collecting extension metadata for
profiler requires ExtensionPolicyService, we have to create it again. But we
cannot create it while XPCOM shutting down. Therefore, we had to skip collecting
extension metadata.

Review commit: https://reviewboard.mozilla.org/r/244356/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/244356/

Comment 4

[Nazım Can Altınova [:canova][:canaltinova on phabricator]]

Hi kmag,
I fixed it with checking if XPCOM is shutting down and if so skipping collecting the extension metadata.
I also tried to figure out and fix the problem fundamentally (about profiler trying to collect metadata very late) for a while. Maybe we can open a new bug for that?

Comment 5

[Kris Maglione [:kmag]]

Comment on attachment 8976155 [details]
Bug 1460697 - Do not collect extension metadata for profiler while XPCOM is shutting down

https://reviewboard.mozilla.org/r/244356/#review250458

Thanks

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c4d7c1c6757e
Do not collect extension metadata for profiler while XPCOM is shutting down r=kmag

Comment 7

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/c4d7c1c6757e