Closed Bug 1141741 Opened 5 years ago Closed 5 years ago

TSan: data race netwerk/dns/nsDNSService2.cpp:693 SetPrefetchEnabled

Categories

(Core :: Networking: DNS, defect)

x86_64
Linux
defect
Not set

Tracking

()

RESOLVED FIXED
mozilla39
Tracking Status
firefox39 --- fixed

People

(Reporter: froydnj, Assigned: bagder)

References

(Blocks 1 open bug)

Details

(Whiteboard: [tsan])

Attachments

(2 files)

Attached file dns-prefetch-race.txt
The attached logfile shows a thread/data race detected by TSan (ThreadSanitizer).

* Specific information about this bug

Not much to say here, looks like a straightforward write-on-one-thread, read-on-another-thread race.  I guess more locking or atomics are the right things to do here?

* 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
I propose simply putting the mDisablePrefetch assignments within the lock already used when it is assigned in other places in this code. See patch.
Comment on attachment 8575954 [details] [diff] [review]
0001-Bug-1141741-make-mDisablePrefetch-assigns-atomic.patch

Review of attachment 8575954 [details] [diff] [review]:
-----------------------------------------------------------------

thanks daniel
Attachment #8575954 - Flags: review+
The try-run seems fine, if we ignore the Mac OS X builds that seem to have gone completely crazy for no apparent reason caused by this patch:

https://treeherder.mozilla.org/#/jobs?repo=try&revision=8cc11b54d8e0
Keywords: checkin-needed
Assignee: nobody → daniel
https://hg.mozilla.org/mozilla-central/rev/2dca9b27c83a
Status: NEW → RESOLVED
Closed: 5 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla39
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