ThreadSanitizer: data race [@ ImageContainer::IPCOpen] vs. [@ ImageBridgeChild::ActorDestroy]
Categories
(Core :: Graphics: Layers, defect, P3)
Tracking
()
People
(Reporter: Gankra, Unassigned)
References
(Blocks 2 open bugs)
Details
(Whiteboard: qa-not-actionable)
Attachments
(1 file)
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39.42 KB,
text/plain
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Details |
The attached crash information was detected while running CI tests with ThreadSanitizer on mozilla-central revision 7167ab3f6e8d7b77439ac1cc7d9356bbaff02510.
Looks like mCanSend needs to be atomic.
Archived lines:
vs
General information about TSan reports
Why fix races?
Data races are undefined behavior and can cause crashes as well as correctness issues. Compiler optimizations can cause racy code to have unpredictable and hard-to-reproduce behavior.
Rating
If you think this race can cause crashes or correctness issues, it would be great to rate the bug appropriately as P1/P2 and/or indicating this in the bug. This makes it a lot easier for us to assess the actual impact that these reports make and if they are helpful to you.
False Positives / Benign Races
Typically, races reported by TSan are not false positives [1], but it is possible that the race is benign. Even in this case it would be nice to come up with a fix if it is easily doable and does not regress performance. Every race that we cannot fix will have to remain on the suppression list and slows down the overall TSan performance. Also note that seemingly benign races can possibly be harmful (also depending on the compiler, optimizations and the architecture) [2][3].
[1] One major exception is the involvement of uninstrumented code from third-party libraries.
[2] http://software.intel.com/en-us/blogs/2013/01/06/benign-data-races-what-could-possibly-go-wrong
[3] How to miscompile programs with "benign" data races: https://www.usenix.org/legacy/events/hotpar11/tech/final_files/Boehm.pdf
Suppressing unfixable races
If the bug cannot be fixed, then a runtime suppression needs to be added in mozglue/build/TsanOptions.cpp. The suppressions match on the full stack, so it should be picked such that it is unique to this particular race. The bug number of this bug should also be included so we have some documentation on why this suppression was added.
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Comment 1•4 years ago
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This seems like either graphics (or maybe media?).
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Comment 2•4 years ago
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This is in ImageBridgeChild, which I think is layers?
mCanSend is a bit redundant with the CanSend() facility provided by IPC, but I don't know if it has the exact same behavior, and I don't think making it use CanSend() would fix the threading issues.
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Reporter | |
Comment 4•4 years ago
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Matt, could you take a look at this?
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Comment 5•4 years ago
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This looks to be benign. We're creating IPC objects from a different thread (using a sync task), so they can racily be shutdown at any time, and that shouldn't be a problem. This check to see if it's already shut down is indeed racy, but shouldn't cause issues.
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Updated•3 years ago
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Updated•2 years ago
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Comment 6•1 year ago
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The fuzzers are reporting this at a low volume.
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Comment 7•1 year ago
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(In reply to Matt Woodrow (:mattwoodrow) from comment #5)
This looks to be benign. We're creating IPC objects from a different thread (using a sync task), so they can racily be shutdown at any time, and that shouldn't be a problem. This check to see if it's already shut down is indeed racy, but shouldn't cause issues.
If the random behavior in itself is okay, then the bools we are racing on here should simply be made atomic to avoid undefined behavior.
Description
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