1660660 - Loading prezi with a gamepad connected on Linux hangs the whole browser.

Status: VERIFIED FIXED

(Core :: DOM: Device Interfaces, defect)

Description

[Emilio Cobos Álvarez [:emilio]]

[Tracking Requested - why for this release]: Full browser DOS, recent regression.

Loading this page (on Linux at least): https://prezi.com/view/THNPJGFVDUCWoM20syev/

Hangs the whole process.

This is a recent regression, I ran mozregression and got:

https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=a8087a6f012c5ac61756aceed9b0c97b7a11493c&tochange=b9e6371846e0ae62c4cd5826c182f7b12eec1620

That sounded pretty strange to me, but turns out I do have an xbox controller connected via USB. And after unplugging and re-opening nightly, loading the page does, in fact, not hang the browser. So it is after all quite likely to be due to that bug.

cmartin, can you take a look?

Comment 1

[Emilio Cobos Álvarez [:emilio]]

Ah, I spotted the bug.

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1660660 - Fix deadlock in gamepad initialization code. r=cmartin

StartGamepadMonitoring() can end up in AddGamepad, and acquire the lock
again on the same thread, effectively dead-locking.

This is a regression from bug 1657404. Relevant stack:

(gdb) bt
#0  0x00007fd19bace801 in clock_nanosleep@GLIBC_2.2.5 () at /lib64/libc.so.6
#1  0x00007fd19bad4157 in nanosleep () at /lib64/libc.so.6
#2  0x00007fd19bad408e in sleep () at /lib64/libc.so.6
#3  0x00007fd195233e87 in ah_crap_handler(int) (signum=11) at /home/emilio/src/moz/gecko-4/toolkit/xre/nsSigHandlers.cpp:95
#4  0x00007fd1952165c4 in nsProfileLock::FatalSignalHandler(int, siginfo_t*, void*) (signo=11, info=0x7fd14abb9db0, context=0x7fd14abb9c80) at /home/emilio/src/moz/gecko-4/toolkit/profile/nsProfileLock.cpp:177
#5  0x00007fd1964973b2 in WasmTrapHandler(int, siginfo_t*, void*) (signum=11, info=<optimized out>, context=<optimized out>) at /home/emilio/src/moz/gecko-4/js/src/wasm/WasmSignalHandlers.cpp:978
#6  0x00007fd19bf3ca90 in <signal handler called> () at /lib64/libpthread.so.0
#7  mozilla::detail::MutexImpl::mutexLock() (this=<optimized out>) at /home/emilio/src/moz/gecko-4/mozglue/misc/Mutex_posix.cpp:118
#8  mozilla::detail::MutexImpl::lock() (this=<optimized out>) at /home/emilio/src/moz/gecko-4/mozglue/misc/Mutex_posix.cpp:142
#9  0x00007fd190cc795a in mozilla::OffTheBooksMutex::Lock() (this=0x7fd136649398) at /home/emilio/src/moz/gecko-4/xpcom/threads/BlockingResourceBase.cpp:318
#10 0x00007fd19326e65e in mozilla::detail::BaseAutoLock<mozilla::Mutex&>::BaseAutoLock(mozilla::Mutex&) (this=<optimized out>, aLock=...) at /home/emilio/src/moz/gecko-4/obj-debug-no-sccache/dist/include/mozilla/Mutex.h:159
#11 mozilla::dom::GamepadPlatformService::NotifyGamepadChange<mozilla::dom::GamepadAdded>(unsigned int, mozilla::dom::GamepadAdded const&) (this=0x7fd136649380, aIndex=1, aInfo=...)
    at /home/emilio/src/moz/gecko-4/dom/gamepad/GamepadPlatformService.cpp:65
#12 0x00007fd193269178 in mozilla::dom::GamepadPlatformService::AddGamepad(char const*, mozilla::dom::GamepadMappingType, mozilla::dom::GamepadHand, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int)
    (this=0x7fd136649380, aID=<optimized out>, aMapping=mozilla::dom::GamepadMappingType::_empty, aHand=mozilla::dom::GamepadHand::_empty, aNumButtons=11, aNumAxes=8, aHaptics=0, aNumLightIndicator=0, aNumTouchEvents=0)
    at /home/emilio/src/moz/gecko-4/dom/gamepad/GamepadPlatformService.cpp:96
#13 0x00007fd19326de4a in (anonymous namespace)::LinuxGamepadService::AddDevice(mozilla::udev_device*) (this=<optimized out>, dev=<optimized out>) at /home/emilio/src/moz/gecko-4/dom/gamepad/linux/LinuxGamepad.cpp:139
#14 0x00007fd19326a156 in (anonymous namespace)::LinuxGamepadService::ScanForDevices() (this=<optimized out>) at /home/emilio/src/moz/gecko-4/dom/gamepad/linux/LinuxGamepad.cpp:188
#15 (anonymous namespace)::LinuxGamepadService::Startup() (this=<optimized out>) at /home/emilio/src/moz/gecko-4/dom/gamepad/linux/LinuxGamepad.cpp:233
#16 mozilla::dom::StartGamepadMonitoring() () at /home/emilio/src/moz/gecko-4/dom/gamepad/linux/LinuxGamepad.cpp:334
#17 0x00007fd193269c6b in mozilla::dom::GamepadPlatformService::AddChannelParent(mozilla::dom::GamepadEventChannelParent*) (this=<optimized out>, aParent=<optimized out>)
    at /home/emilio/src/moz/gecko-4/dom/gamepad/GamepadPlatformService.cpp:225
#18 0x00007fd19326d175 in mozilla::dom::GamepadEventChannelParent::Init() (this=0x7fd136e76a00) at /home/emilio/src/moz/gecko-4/dom/gamepad/ipc/GamepadEventChannelParent.cpp:50
#19 0x00007fd1913ba3a6 in mozilla::ipc::BackgroundParentImpl::RecvPGamepadEventChannelConstructor(mozilla::dom::PGamepadEventChannelParent*) (this=0x7fd13f888000, aActor=0x0)
    at /home/emilio/src/moz/gecko-4/ipc/glue/BackgroundParentImpl.cpp:1109
#20 0x00007fd1917c7da1 in mozilla::ipc::PBackgroundParent::OnMessageReceived(IPC::Message const&) (this=0x7fd13f888000, msg__=...) at PBackgroundParent.cpp:4967
#21 0x00007fd1913ea71d in mozilla::ipc::MessageChannel::DispatchAsyncMessage(mozilla::ipc::ActorLifecycleProxy*, IPC::Message const&) (this=0x7fd13f8880f8, aProxy=0x7fd13ff48140, aMsg=...)

Comment 3

[Chris Martin [:cmartin]]

Thanks for the regression and quick fix, :emilio!

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/b538d853d883
Fix deadlock in gamepad initialization code. r=cmartin

Comment 5

[Emilio Cobos Álvarez [:emilio]]

Comment on attachment 9171565 [details]
Bug 1660660 - Fix deadlock in gamepad initialization code. r=cmartin

Beta/Release Uplift Approval Request

• User impact if declined: Deadlocks on linux on some pages with a gamepad connected.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: comment 0, though I can verify myself I guess.
• List of other uplifts needed: none
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Simple patch to restore to the previous behavior.
• String changes made/needed: none

Comment 6

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/b538d853d883

Comment 7

[Cornel Ionce [:noni]]

Confirming this no longer reproduces on Ubuntu 20.04 using latest Nightly (build ID 20200824215021).

Comment 8

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9171565 [details]
Bug 1660660 - Fix deadlock in gamepad initialization code. r=cmartin

Approved for 81.0b2.

Comment 9

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-beta/rev/d21db70d7bac

Comment 10

[Cornel Ionce [:noni]]

I can also confirm that I see no crash on Fx 81.0b2, build ID 20200825191644.