1686153 - ThreadSanitizer: data race [@ SkARGB32_Black_Blitter::blitAntiH] vs. [@ mozilla::layers::MemoryTextureData::Create]

Status: RESOLVED DUPLICATE of bug 1601600

(Core :: Graphics: Layers, defect)

Description

[Tyson Smith [:tsmith]]

Attachment: Detailed Crash Information

The attached crash information was detected by ThreadSanitizer while fuzzing with build mozilla-central 20210111-7643eaee62a3. The fuzzers have hit this issue multiple times but no reliable test case is available at this time.

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

[Aria Beingessner [:Gankra]]

whoops, sorry ignore the previous version of the comment, posted on the wrong bug.

Comment 2

[Tyson Smith [:tsmith]]

Attachment: Detailed Crash Information

This report has stacks from both of the racing threads.

Comment 3

[Aria Beingessner [:Gankra]]

So I think all of these bugs are the same issue, and none of them need to be security since they're just racing on the colors of a texture while it's being uploaded to the gpu:

• Bug 1686637
• Bug 1686153
• Bug 1656326
• (probably, missing stack) Bug 1647398
• (maybe, not uploading but similar) Bug 1601600

(I don't appear to have permissions to de-security these bugs...)

Bug 1601600 already has many supressions, which is probably why it's so hard to reproduce the others -- usually tsan will see the race in one of those functions and discard it.

Possibly they should all be closed as dupes of Bug 1601600, maybe with more suppressions added.