[Webkit-unassigned] [Bug 209437] New: Assertion triggered on iOS 13: Multiple locks on web thread

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=209437

            Bug ID: 209437
           Summary: Assertion triggered on iOS 13: Multiple locks on web
                    thread
           Product: WebKit
           Version: Safari 13
          Hardware: iPhone / iPad
                OS: iOS 13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: darrenmo at google.com

Created attachment 394302

  --> https://bugs.webkit.org/attachment.cgi?id=394302&action=review

Stack trace on (iPhone9,3 13.3.1 17D50)

Starting in iOS 13 and still occurring in iOS 13.4, an assertion in `_WebThreadLock` is being hit: `Multiple locks on web thread not allowed! Please file a bug. Crashing now...`.

The attached stack trace points to the following `WebCore` code:
```
                     __ZL14_WebThreadLockv.cold.1:        // _WebThreadLock() [clone .cold.1]
0000000189ab5708         sub        sp, sp, #0x20                               ; CODE XREF=__ZL14_WebThreadLockv+336
0000000189ab570c         stp        x29, x30, [sp, #0x10]
0000000189ab5710         add        x29, sp, #0x10
0000000189ab5714         bl         __ZL20CurrentThreadContextv                 ; CurrentThreadContext()
0000000189ab5718         adrp       x8, #0x189b51000                            ; 0x189b51340 at PAGE
0000000189ab571c         add        x8, x8, #0x340                              ; 0x189b51340 at PAGEOFF, "void _WebThreadLock()"
0000000189ab5720         stp        x8, x0, [sp]
0000000189ab5724         adrp       x0, #0x1bf154000                            ; 0x1bf154850 at PAGE
0000000189ab5728         add        x0, x0, #0x850                              ; 0x1bf154850 at PAGEOFF, @"%s, %p: Multiple locks on web thread not allowed! Please file a bug. Crashing now..."
0000000189ab572c         bl         imp___stubs___ZNK2sh14TConstantUniongtERKS0_ ; sh::TConstantUnion::operator>(sh::TConstantUnion const&) const
0000000189ab5730         brk        #0x0
0000000189ab5734         brk        #0x1
```

We do not have information about what was happening in the app prior to the crash aside from the attached stack trace.

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