1805796 - Assertion failure: gNeckoChild, at netwerk/base/Predictor.cpp:1242

Status: RESOLVED FIXED

(Core :: Networking, defect, P3)

Description

[Daniel Holbert [:dholbert]]

I just happened to hit this fatal assertion, in a local debug build, which I was only running for a few seconds:

[Child 289686, Main Thread] WARNING: NS_ENSURE_TRUE(gNeckoChild != nullptr) failed: file netwerk/protocol/http/HttpChannelChild.cpp:2008
Assertion failure: gNeckoChild, at netwerk/base/Predictor.cpp:1242

I started the build via ./mach run (with no existing profile, so one was created for me); I visited about:config, did a Ctrl+P print operation, and by that point this fatal assertion was already in my terminal output; though I didn't get any sort of crash UI or visible breakage in Firefox itself.

Fortunately I captured it in rr (since I was recording to capture a different bug) and I'll submit it to pernosco.

Comment 1

[Daniel Holbert [:dholbert]]

I'm running an up-to-date debug build, from revision https://hg.mozilla.org/mozilla-central/rev/7ff758e0d08b .

Here's the backtrace (run through fix_stacks.py):

[Child 289686, Main Thread] WARNING: NS_ENSURE_TRUE(gNeckoChild != nullptr) failed: file /scratch/work/builds/mozilla-central/mozilla/netwerk/protocol/http/HttpChannelChild.cpp:2008
Assertion failure: gNeckoChild, at /scratch/work/builds/mozilla-central/mozilla/netwerk/base/Predictor.cpp:1242
#01: mozilla::net::Predictor::LearnNative(nsIURI*, nsIURI*, unsigned int, mozilla::OriginAttributes const&) (/scratch/work/builds/mozilla-central/mozilla/netwerk/base/Predictor.cpp:1242)
#02: mozilla::net::PredictorLearn(nsIURI*, nsIURI*, unsigned int, nsILoadGroup*) (/scratch/work/builds/mozilla-central/mozilla/netwerk/base/Predictor.cpp:1996)
#03: mozilla::dom::FontFaceSetDocumentImpl::StartLoad(gfxUserFontEntry*, unsigned int) (/scratch/work/builds/mozilla-central/mozilla/layout/style/FontFaceSetDocumentImpl.cpp:321)
#04: gfxUserFontEntry::DoLoadNextSrc(bool) (/scratch/work/builds/mozilla-central/mozilla/gfx/thebes/gfxUserFontSet.cpp:547)
#05: gfxUserFontEntry::LoadNextSrc() (/scratch/work/builds/mozilla-central/mozilla/gfx/thebes/gfxUserFontSet.cpp:380)
#06: gfxUserFontEntry::FontLoadFailed(nsIFontLoadCompleteCallback*) (/scratch/work/builds/mozilla-central/mozilla/gfx/thebes/gfxUserFontSet.cpp:0)
#07: gfxUserFontEntry::FontDataDownloadComplete(unsigned int, unsigned char const*, unsigned int, nsresult, nsIFontLoadCompleteCallback*) (/scratch/work/builds/mozilla-central/mozilla/gfx/thebes/gfxUserFontSet.cpp:865)
#08: nsFontFaceLoader::OnStreamComplete(nsIStreamLoader*, nsISupports*, nsresult, unsigned int, unsigned char const*) (/scratch/work/builds/mozilla-central/mozilla/layout/style/nsFontFaceLoader.cpp:299)
#09: mozilla::net::nsStreamLoader::OnStopRequest(nsIRequest*, nsresult) (/scratch/work/builds/mozilla-central/mozilla/netwerk/base/nsStreamLoader.cpp:85)
#10: nsCORSListenerProxy::OnStopRequest(nsIRequest*, nsresult) (/scratch/work/builds/mozilla-central/mozilla/netwerk/protocol/http/nsCORSListenerProxy.cpp:677)
#11: mozilla::net::HttpChannelChild::DoOnStopRequest(nsIRequest*, nsresult) (/scratch/work/builds/mozilla-central/mozilla/netwerk/protocol/http/HttpChannelChild.cpp:1055)
#12: mozilla::net::HttpChannelChild::OnStopRequest(nsresult const&, mozilla::net::ResourceTimingStructArgs const&, mozilla::net::nsHttpHeaderArray const&) (/scratch/work/builds/mozilla-central/mozilla/netwerk/protocol/http/HttpChannelChild.cpp:933)
#13: mozilla::net::HttpChannelChild::ProcessOnStopRequest(nsresult const&, mozilla::net::ResourceTimingStructArgs const&, mozilla::net::nsHttpHeaderArray const&, nsTArray<mozilla::net::ConsoleReportCollected>&&, bool)::$_23::operator()() (/scratch/work/builds/mozilla-central/mozilla/netwerk/protocol/http/HttpChannelChild.cpp:805)
#14: std::_Function_handler<void (), mozilla::net::HttpChannelChild::ProcessOnStopRequest(nsresult const&, mozilla::net::ResourceTimingStructArgs const&, mozilla::net::nsHttpHeaderArray const&, nsTArray<mozilla::net::ConsoleReportCollected>&&, bool)::$_23>::_M_invoke(std::_Any_data const&) (/scratch/work/builds/.mozbuild/sysroot-x86_64-linux-gnu/usr/include/c++/7.5.0/bits/std_function.h:318)
#15: std::function<void ()>::operator()() const (/scratch/work/builds/.mozbuild/sysroot-x86_64-linux-gnu/usr/include/c++/7.5.0/bits/std_function.h:706)
#16: mozilla::net::ChannelFunctionEvent::Run() (/scratch/work/builds/mozilla-central/obj-debug/dist/include/mozilla/net/ChannelEventQueue.h:55)
#17: mozilla::net::ChannelEventQueue::FlushQueue() (/scratch/work/builds/mozilla-central/mozilla/netwerk/ipc/ChannelEventQueue.cpp:95)
#18: mozilla::net::ChannelEventQueue::MaybeFlushQueue() (/scratch/work/builds/mozilla-central/obj-debug/dist/include/mozilla/net/ChannelEventQueue.h:0)
#19: mozilla::net::ChannelEventQueue::CompleteResume() (/scratch/work/builds/mozilla-central/mozilla/netwerk/ipc/ChannelEventQueue.h:0)
#20: mozilla::net::ChannelEventQueue::ResumeInternal()::CompleteResumeRunnable::Run() (/scratch/work/builds/mozilla-central/mozilla/netwerk/ipc/ChannelEventQueue.cpp:153)
#21: mozilla::SchedulerGroup::Runnable::Run() (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/SchedulerGroup.cpp:140)
#22: mozilla::RunnableTask::Run() (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/TaskController.cpp:539)
#23: mozilla::TaskController::DoExecuteNextTaskOnlyMainThreadInternal(mozilla::detail::BaseAutoLock<mozilla::Mutex&> const&) (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/TaskController.cpp:852)
#24: mozilla::TaskController::ExecuteNextTaskOnlyMainThreadInternal(mozilla::detail::BaseAutoLock<mozilla::Mutex&> const&) (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/TaskController.cpp:684)
#25: mozilla::TaskController::ProcessPendingMTTask(bool) (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/TaskController.cpp:462)
#26: mozilla::TaskController::InitializeInternal()::$_2::operator()() const (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/TaskController.cpp:188)
#27: mozilla::detail::RunnableFunction<mozilla::TaskController::InitializeInternal()::$_2>::Run() (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/nsThreadUtils.h:547)
#28: nsThread::ProcessNextEvent(bool, bool*) (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/nsThread.cpp:1207)
#29: NS_ProcessNextEvent(nsIThread*, bool) (/scratch/work/builds/mozilla-central/mozilla/xpcom/threads/nsThreadUtils.cpp:474)
#30: mozilla::ipc::MessagePump::Run(base::MessagePump::Delegate*) (/scratch/work/builds/mozilla-central/mozilla/ipc/glue/MessagePump.cpp:85)
#31: mozilla::ipc::MessagePumpForChildProcess::Run(base::MessagePump::Delegate*) (/scratch/work/builds/mozilla-central/mozilla/ipc/glue/MessagePump.cpp:269)
#32: MessageLoop::RunInternal() (/scratch/work/builds/mozilla-central/mozilla/ipc/chromium/src/base/message_loop.cc:381)
#33: MessageLoop::RunHandler() (/scratch/work/builds/mozilla-central/mozilla/ipc/chromium/src/base/message_loop.cc:375)
#34: MessageLoop::Run() (/scratch/work/builds/mozilla-central/mozilla/ipc/chromium/src/base/message_loop.cc:356)
#35: nsBaseAppShell::Run() (/scratch/work/builds/mozilla-central/mozilla/widget/nsBaseAppShell.cpp:152)
#36: XRE_RunAppShell() (/scratch/work/builds/mozilla-central/mozilla/toolkit/xre/nsEmbedFunctions.cpp:884)
#37: mozilla::ipc::MessagePumpForChildProcess::Run(base::MessagePump::Delegate*) (/scratch/work/builds/mozilla-central/mozilla/ipc/glue/MessagePump.cpp:235)
#38: MessageLoop::RunInternal() (/scratch/work/builds/mozilla-central/mozilla/ipc/chromium/src/base/message_loop.cc:381)
#39: MessageLoop::RunHandler() (/scratch/work/builds/mozilla-central/mozilla/ipc/chromium/src/base/message_loop.cc:375)
#40: MessageLoop::Run() (/scratch/work/builds/mozilla-central/mozilla/ipc/chromium/src/base/message_loop.cc:356)
#41: XRE_InitChildProcess(int, char**, XREChildData const*) (/scratch/work/builds/mozilla-central/mozilla/toolkit/xre/nsEmbedFunctions.cpp:747)
#42: mozilla::BootstrapImpl::XRE_InitChildProcess(int, char**, XREChildData const*) (/scratch/work/builds/mozilla-central/mozilla/toolkit/xre/Bootstrap.cpp:67)
#43: content_process_main(mozilla::Bootstrap*, int, char**) (/scratch/work/builds/mozilla-central/mozilla/ipc/contentproc/plugin-container.cpp:57)
#44: main (/scratch/work/builds/mozilla-central/mozilla/browser/app/nsBrowserApp.cpp:359)
#45: ??? (/lib/x86_64-linux-gnu/libc.so.6 + 0x29d90)
#46: __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6 + 0x29e40)
#47: ??? (/scratch/work/builds/mozilla-central/obj-debug/dist/bin/firefox + 0x869d9)
#48: ??? (???:???)

Comment 2

[Daniel Holbert [:dholbert]]

Pernosco trace: https://pernos.co/debug/MS3nZ4Bz4afyPsJ4_b1aBg/index.html

Comment 3

[Kershaw Chang [:kershaw]]

Looks like we are trying to do predict during shutdown.

Comment 4

[Daniel Holbert [:dholbert]]

RE shutdown: just to clarify, I didn't explicitly quit/shutdown Firefox here. (Maybe you're referring to a helper process shutting down in the background though.)

Comment 5

[Tyson Smith [:tsmith]]

Found with m-c 20240102-60c369c930dc (--enable-debug --enable-fuzzing).

This was detected by live site testing. It can be reliably triggered by visiting http://bergfex.at/ with a debug build.

Comment 6

[Tyson Smith [:tsmith]]

A Pernosco session is available here: https://pernos.co/debug/YLSMkV4iK3vh_UjiKqNz9g/index.html

Comment 7

[Kershaw Chang [:kershaw]]

We will try to fix this soon.

Comment 8

[Valentin Gosu [:valentin] (he/him)]

I haven't looked at the pernosco trace yet, but PredictorLearnRunnable::Run does an early return if gNeckoChild is null.
It would be good to confirm there isn't something weird going on, but I think the solution will be to just remove the assert

Comment 9

[Kershaw Chang [:kershaw]]

Attachment: Bug 1805796 - Remove MOZ_DIAGNOSTIC_ASSERT(gNeckoChild), r=#necko

The Pernosco session shows that the content child is about to destroy at that point, so there is not much we can do.
Removing the diagnostic assert seems to be the only way.

Comment 10

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5512c3ec56fc
Remove MOZ_DIAGNOSTIC_ASSERT(gNeckoChild), r=necko-reviewers,valentin

Comment 11

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/5512c3ec56fc