1655518 - ThreadSanitizer: data race [@ WebCore::ReverbConvolver::backgroundThreadEntry] vs. [@ WebCore::ReverbConvolver::~ReverbConvolver]

Status: RESOLVED FIXED

(Core :: Web Audio, defect, P3)

Description

[Jason Kratzer [:jkratzer]]

Attachment: log_ffp_asan_18574.log.18864.txt

The attached crash information was detected while running CI tests with ThreadSanitizer on mozilla-central revision 20200727-798bdad605b9.

For detailed crash information, see attachment.
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.

Comment 1

[Jason Kratzer [:jkratzer]]

Attachment: testcase.html

Comment 2

[Paul Adenot (:padenot)]

Attachment: Bug 1655518 - Make two bool in ReverbConvolver atomic. r?karlt

The code structure is strange. This will be enough to make this safe without
fear of changing the behaviour.

Comment 3

[Karl Tomlinson (:karlt)]

Write to m_wantsToExit in ~ReverbConvolver:
Read from m_wantsToExit in backgroundThreadEntry().

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8f55969cc058
Make two bool in ReverbConvolver atomic. r=karlt

Comment 5

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/8f55969cc058