1136849 - TSan: data race image/src/imgRequestProxy.cpp:90 GetProgressTracker

Status: RESOLVED FIXED

(Core :: Graphics: ImageLib, defect)

Description

[Nathan Froyd [:froydnj]]

Attachment: imgrequestproxy-race.txt

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

* Specific information about this bug

I do not understand the stacks here at all.  The line for the writing stack implicates nsRefPtr::take, but the offending caller in ProxyListener::OnDataAvailable is merely making a virtual method call, and so shouldn't be calling |take()|.  The line for the reading stack implicates a read on RequestBehavior::mOwner, which seems weird.

I don't think we have to worry about inlining on the write (since virtual methods aren't going to be inlined, presumably) or on the read (RequestBehavior::GetProgressTracker calls into imageRequest::GetProgressTracker, which is out-of-line).

Ideas here welcome.

* 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

[Seth Fowler [:seth] [:s2h]]

Fixed in bug 1137002.