967544 - TSan: data race js/src/../../js/src/shell/js.cpp:2990 CancelExecution

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Christian Holler (:decoder)]

Attachment: Logfile with TSan trace

The attached logfile shows a thread/data race (mozilla-central revision 44ba69cacd7e) detected by TSan (ThreadSanitizer).

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 inacceptable performance issues. Also note that seemingly benign races can possibly be harmful (also depending on the compiler and the architecture) [1].

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

Comment 1

[Jan de Mooij [:jandem]]

This one is for the shell's gTimedOut global. We can just make that a mozilla::Atomic I think, just like JSRuntime::interrupt.

Comment 2

[Jan de Mooij [:jandem]]

(In reply to Christian Holler (:decoder) from comment #1)
> I think this is the same problem as in bug 967544, but racing for
> gTimeoutFunc instead of gTimedOut. gTimeoutFunc is a JS::Value, how would we
> solve that issue here?

gTimeoutFunc Value is either a NullValue() or ObjectValue(), so I think you could make it a JSObject* instead (and use nullptr instead of NullValue()). Does that help?

Comment 3

[Nathan Froyd [:froydnj]]

Still happening; I'm going to fix this, as it makes TSan testing with the shell unpleasant.  Also, less use of |volatile| in the codebase can't be a bad thing.

Comment 4

[Nathan Froyd [:froydnj]]

Attachment: make gServiceInterrupt Atomic

|volatile| doesn't guarantee inter-thread safety.  Atomic<> does.

Atomic<> also makes TSan much happier.

Comment 5

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/007b21fc06a3

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/007b21fc06a3