1623034 - ThreadSanitizer: data race [@ QuitProgressUI] vs. [@ ShowProgressUI] in updater

Status: RESOLVED FIXED

(Toolkit :: Application Update, defect, P3)

Description

[Christian Holler (:decoder)]

The attached crash information was detected while running CI tests with ThreadSanitizer on try revision bdca0035b64681e8ce1be97aef3490118dde2a00 (this is from a try run made by :egao on Ubuntu 18.04).

This looks like a simple global boolean. We are accessing and writing sQuit without synchronization (there is a sleep inbetween instead).

To fix this, sQuit should be an Atomic.

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

[Christian Holler (:decoder)]

Attachment: Detailed Crash Information

Comment 2

[Jayati Shrivastava]

Hi! May I work on this? :)

Comment 3

[Molly Howell (she/her) (mostly inactive)]

Of course, please do! The description here has the info about what needs to be done and why, but to provide a little more detail: this declaration of sQuit needs to be a mozilla::Atomic<gboolean> instead of just a gboolean. You'll have to add an include for mozilla/Atomics.h to get the Atomic type definition.

Comment 4

[Jayati Shrivastava]

Attachment: Bug 1623034 - Changed sQuit from gboolean to mozilla::Atomic<gboolean>. r=mhowell

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/ea74f7a4ea71
Changed sQuit from gboolean to mozilla::Atomic<gboolean>. r=mhowell

Comment 6

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/ea74f7a4ea71