967455 - TSan: data race js/src/../../js/src/jsscript.h:1105 canIonCompile

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 tsan-trace1.txt) 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 one purpose I think, see JSScript::hasIonScript:

        // Note: While a script's baseline script is protected by the
        // compilation lock, writes to the ion script are not. This helps lock
        // ordering issues in CodeGenerator::link. Tests of script->ion during
        // off thread compilation can therefore race, though these are fairly
        // benign and the IonScript itself is never accessed.

It'd be nice if we could avoid this though...

Comment 2

[Christian Holler (:decoder)]

m-c revision for the trace is 44ba69cacd7e, my script messed that up somehow.

Comment 3

[Christian Holler (:decoder)]

This was fixed by the backout of bug 785905.