1153394 - TSan: data race dom/ipc/ProcessHangMonitor.cpp:98 HangMonitorChild::Get()

Status: RESOLVED FIXED

(Core :: DOM: Content Processes, defect)

Description

[Nathan Froyd [:froydnj]]

Attachment: dom-ipc-hangmonitor.txt

The attached logfile shows a thread/data race detected by TSan (ThreadSanitizer).

* Specific information about this bug

This race looks like we're relying on a variable getting set on one thread and being able to be read in another.  Turning this variable into an Atomic<> is probably the right thing to do.

* General information about TSan, data races, etc.

Typically, races reported by TSan are not false positives, but it is possible that the race is benign. Even in this case though, we should try to come up with a fix unless this would cause unacceptable performance issues. Also note that seemingly benign races can possibly be harmful (also depending on the compiler and the architecture) [1][2].

If the bug cannot be fixed, then this bug should be used to either make a compile-time annotation for blacklisting or add an entry to the runtime blacklist.

[1] http://software.intel.com/en-us/blogs/2013/01/06/benign-data-races-what-could-possibly-go-wrong
[2] _How to miscompile programs with "benign" data races_: https://www.usenix.org/legacy/events/hotpar11/tech/final_files/Boehm.pdf

Comment 1

[Nathan Froyd [:froydnj]]

Attachment: make HangMonitorChild::sInstance an atomic variable

The atomic-ness here should not be significant performance concern--it looks
like we're not accessing this variable in hot paths.

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Comment on attachment 8659965 [details] [diff] [review]
make HangMonitorChild::sInstance an atomic variable

Review of attachment 8659965 [details] [diff] [review]:
-----------------------------------------------------------------

Thanks Nathan.

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/c425e00cb6c5

Comment 4

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/c425e00cb6c5