[BUG] Crash in FIRRemoteConfig.m

[KabukiAdam]

[REQUIRED] Step 2: Describe your environment

• Xcode version: 11.1
• Firebase SDK version: 6.10.0
• Firebase Component: Remote Config
• Component version: 4.4.3

[REQUIRED] Step 3: Describe the problem

After releasing the latest update to our app, we've started to see this crash in the crash logs.
Seems to be affecting about 5% of users.
Happens on both iOS 12 and iOS 13 devices.

I saw some other Remote Config crashes when I searched the github issues, but I didn't see any with this particular stack trace (or similar).

BUG IN CLIENT OF LIBDISPATCH: dispatch_sync called on queue already owned by current thread

Stack trace:

Crashed: com.google.GoogleConfigService.FIRRemoteConfig
0  libdispatch.dylib              0x1bbfae0f4 __DISPATCH_WAIT_FOR_QUEUE__ + 448
1  libdispatch.dylib              0x1bbfadc84 _dispatch_sync_f_slow + 140
2  Flow                           0x10107b610 -[FIRRemoteConfig lastFetchStatus] + 438 (FIRRemoteConfig.m:438)
3  Flow                           0x10101cc88 -[FPRRemoteConfigFlags performanceSDKEnabled] + 4376562824
4  Flow                           0x10101ae24 -[FPRConfigurations sdkEnabled] + 4376555044
5  Flow                           0x101026df8 -[FPRNetworkTrace initWithURLRequest:] + 4376604152
6  Flow                           0x10102e8f4 __InstrumentDataTaskWithRequestCompletionHandler_block_invoke + 4376635636
7  Flow                           0x10102e88c __InstrumentDataTaskWithRequestCompletionHandler_block_invoke + 4376635532
8  Flow                           0x101006bdc -[FIRInstanceIDCheckinService checkinWithExistingCheckin:completion:] + 189 (FIRInstanceIDCheckinService.m:189)
9  Flow                           0x101004a04 -[FIRInstanceIDAuthService fetchCheckinInfoWithHandler:] + 188 (FIRInstanceIDAuthService.m:188)
10 Flow                           0x100ffe354 -[FIRInstanceID tokenWithAuthorizedEntity:scope:options:handler:] + 367 (FIRInstanceID.m:367)
11 Flow                           0x1010882e0 -[RCNConfigFetch refreshInstanceIDTokenAndFetchCheckInInfoWithCompletionHandler:] + 251 (RCNFetch.m:251)
12 Flow                           0x101087f70 __74-[RCNConfigFetch fetchAllConfigsWithExpirationDuration:completionHandler:]_block_invoke + 190 (RCNFetch.m:190)
13 libdispatch.dylib              0x1bbfc9610 _dispatch_call_block_and_release + 24
14 libdispatch.dylib              0x1bbfca184 _dispatch_client_callout + 16
15 libdispatch.dylib              0x1bbfa773c _dispatch_lane_serial_drain$VARIANT$armv81 + 564
16 libdispatch.dylib              0x1bbfa8154 _dispatch_lane_invoke$VARIANT$armv81 + 400
17 libdispatch.dylib              0x1bbfb143c _dispatch_workloop_worker_thread + 576
18 libsystem_pthread.dylib        0x1bc019fa4 _pthread_wqthread + 276
19 libsystem_pthread.dylib        0x1bc01cae0 start_wqthread + 8

I spent a bit of time looking through the source code related to the stack trace, and I can see how the error happens. It looks like [RCNConfigFetch fetchAllConfigsWithExpirationDuration:completionHandler:] does its work on the same dispatch queue that [FIRRemoteConfig lastFetchStatus] uses for its dispatch_sync() call.

I realize that we're a version or two behind on the Firebase SDK. I looked at the release notes and source diff and didn't see anything that looked like a fix for this, but if I'm wrong and updating the SDK will fix this, please let me know. 😄

[google-oss-bot]

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[paulb777]

This is likely related to the other crashes involving FirebasePerformance and FirebaseRemoteConfig.

[visumickey]

This issue is fixed and will be rolled out in the upcoming release of Firebase Performance.

[ryanwilson]

Firebase 6.13.0 was just released and should address this issue. Please update and re-open if you're still seeing the issue, thanks!

[siburb]

Hi @ryanwilson. I work with @KabukiAdam and can confirm that we're still seeing this same crash in the latest release of our app. It is using Firebase 6.13.0, so this issue is not fixed.

[visumickey]

@siburb
Can you share the version of Firebase Performance you are using (Podfile.lock should contain it). Can you also add a copy of the most recent crash logs you see as a part of 6.13.0?

[siburb]

Thanks @visumickey - this is our number 1 crash at the moment, we could do with a fix asap.

Here's the trace from thread 9 of an example crash - I can send you the whole log directly if necessary?

Crashed: com.google.GoogleConfigService.FIRRemoteConfig
0  libdispatch.dylib              0x1c04b30e4 __DISPATCH_WAIT_FOR_QUEUE__ + 448
1  libdispatch.dylib              0x1c04b2c74 _dispatch_sync_f_slow + 140
2  Actions                        0x1007690d8 -[FIRRemoteConfig lastFetchStatus] + 438 (FIRRemoteConfig.m:438)
3  Actions                        0x10070a790 -[FPRRemoteConfigFlags performanceSDKEnabled] + 4310116240
4  Actions                        0x10070892c -[FPRConfigurations sdkEnabled] + 4310108460
5  Actions                        0x100714900 -[FPRNetworkTrace initWithURLRequest:] + 4310157568
6  Actions                        0x10071c3fc __InstrumentDataTaskWithRequestCompletionHandler_block_invoke + 4310189052
7  Actions                        0x10071c394 __InstrumentDataTaskWithRequestCompletionHandler_block_invoke + 4310188948
8  Actions                        0x1006d56fc -[FIRInstanceIDCheckinService checkinWithExistingCheckin:completion:] + 189 (FIRInstanceIDCheckinService.m:189)
9  Actions                        0x1006d3524 -[FIRInstanceIDAuthService fetchCheckinInfoWithHandler:] + 188 (FIRInstanceIDAuthService.m:188)
10 Actions                        0x1006cc1d4 -[FIRInstanceID(Private) fetchCheckinInfoWithHandler:] + 35 (FIRInstanceID+Private.m:35)
11 Actions                        0x100776338 -[RCNConfigFetch fetchCheckinInfoWithCompletionHandler:] + 289 (RCNFetch.m:289)
12 Actions                        0x100776270 __81-[RCNConfigFetch refreshInstanceIDTokenAndFetchCheckInInfoWithCompletionHandler:]_block_invoke.146 + 246 (RCNFetch.m:246)
13 libdispatch.dylib              0x1c04ce610 _dispatch_call_block_and_release + 24
14 libdispatch.dylib              0x1c04cf184 _dispatch_client_callout + 16
15 libdispatch.dylib              0x1c04ac710 _dispatch_lane_serial_drain$VARIANT$armv81 + 564
16 libdispatch.dylib              0x1c04ad128 _dispatch_lane_invoke$VARIANT$armv81 + 400
17 libdispatch.dylib              0x1c04b643c _dispatch_workloop_worker_thread + 576
18 libsystem_pthread.dylib        0x1c051ef88 _pthread_wqthread + 276
19 libsystem_pthread.dylib        0x1c0521ad4 start_wqthread + 8

Crashlytics also shows the following:
"BUG IN CLIENT OF LIBDISPATCH: dispatch_sync called on queue already owned by current thread"

Here's an extract from "podfile.lock":

  - Firebase/Performance (6.13.0):
    - Firebase/CoreOnly
    - FirebasePerformance (~> 3.1.7)

<other stuff>

  - FirebasePerformance (3.1.7):
    - FirebaseCore (~> 6.4)
    - FirebaseInstanceID (~> 4.2)
    - FirebaseRemoteConfig (~> 4.4)
    - GoogleToolboxForMac/Logger (~> 2.1)
    - "GoogleToolboxForMac/NSData+zlib (~> 2.1)"
    - GoogleUtilities/Environment (~> 6.2)
    - GoogleUtilities/ISASwizzler (~> 6.2)
    - GoogleUtilities/MethodSwizzler (~> 6.2)
    - GTMSessionFetcher/Core (~> 1.1)
    - Protobuf (~> 3.9)