[Webkit-unassigned] [Bug 64779] New: Yielding the parser for first paint causes problems with <svg><use><script>

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=64779

           Summary: Yielding the parser for first paint causes problems
                    with <svg><use><script>
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: simonjam at chromium.org
                CC: inferno at chromium.org, tonyg at chromium.org
            Blocks: 64419


If bug 64419 is fixed, svg/dom/use-style-recalc-script-execute-crash.html will start crashing.

The problem is that the parser yields after parsing the second </script>, but before executing it. The parser is yielding to allow the first paint to occur. When the parser yields, recalcStyle() will process the <svg use> tag and build a shadow DOM for it. The shadow DOM clones the elements from the main DOM. This includes the parsed, but un-executed, second script. The cloned script will execute, because its m_alreadyStarted is false, when it's inserted in the shadow DOM. When control returns to the parser, it will execute the original script. So, we'll have executed the same block of script twice.

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