1816713 - ThreadSanitizer: data race [@ pthread_barrier_destroy] vs. [@ pthread_barrier_wait]

Status: RESOLVED FIXED

(Core :: Graphics: WebGPU, defect, P1)

Description

[Jason Kratzer [:jkratzer]]

The attached crash information was detected while fuzzing with ThreadSanitizer on mozilla-central revision 20230214-f45ac8766b61.

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: Detailed Crash Information

Comment 2

[Christian Holler (:decoder)]

This is likely a false-positive, the second stack has an uninstrumented dso (libvulkan_lvp.so) that we probably need to add to the suppression dso list.

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

This bug prevents fuzzing from making progress; however, it has low severity. It is important for fuzz blocker bugs to be addressed in a timely manner (see here why?).
:jimb, could you increase the severity?

For more information, please visit auto_nag documentation.

Comment 4

[Jim Blandy :jimb]

Marking S3 because WebGPU is not yet enabled.
Marking P1 because fuzzblockers are bad for enabling WebGPU.

Comment 5

[Christian Holler (:decoder)]

(In reply to Christian Holler (:decoder) from comment #2)

This is likely a false-positive, the second stack has an uninstrumented dso (libvulkan_lvp.so) that we probably need to add to the suppression dso list.

Jason, can you make a patch based on this? Just add the relevant DSO to the called_from_lib list in https://searchfox.org/mozilla-central/source/mfbt/TsanOptions.h

Comment 6

[Jason Kratzer [:jkratzer]]

Attachment: Bug 1816713 - Add libvulkan to thread sanitizer suppression list r=decoder

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/fe8b2fd55315
Add libvulkan to thread sanitizer suppression list r=decoder

Comment 8

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/fe8b2fd55315