1141692 - TSan: data race xpcom/threads/nsThreadPool.cpp:153 Run

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Nathan Froyd [:froydnj]]

Attachment: thread-pool-naming.txt

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

* Specific information about this bug

AFAICT, this race actually comes from this bit of code:

http://mxr.mozilla.org/mozilla-central/source/xpcom/glue/nsThreadUtils.cpp#328

with unified sources contributing to the inlining of that function into nsThreadPool::Run, and inlined methods contributing to nsTSubstring::AppendInt getting dinged as the actual location of the race in the logfile.

Anyway, mCounter is |volatile|, which is just silly.  Let's fix that.
* 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: use an actual Atomic for nsThreadPoolNaming::mCounter

Marking a variable as volatile is never the right thing to do when
dealing with threads.  Use real atomic accesses instead.

Comment 2

[Benjamin Smedberg]

Comment on attachment 8575465 [details] [diff] [review]
use an actual Atomic for nsThreadPoolNaming::mCounter

Blech, I truly detest atomicity being only part of the type system and not explicitly visible at callsites :-(

Comment 3

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/421e7047df36