Bug 136326 – Crash in new multicolumn code when interacting with position: absolute

• Component: MathML
• Status: RESOLVED FIXED

[Vicki Pfau]

Created attachment 237277 [details]
Repro

The attached simple test case will cause ToT to crash with a null deref. The test case appears to involve creating a MathML element with position: absolute that interacts poorly with the new multicolumn code. A debug build spits out the following backtrace when it hits an assertion:

ASSERTION FAILED: isRenderView() || (region && flowThread)
/Volumes/Share/Safari/Staging/Source/WebCore/rendering/RenderBox.cpp(140) : WebCore::RenderRegion *WebCore::RenderBox::clampToStartAndEndRegions(WebCore::RenderRegion *) const
1   0x10f1ef790 WTFCrash
2   0x113fc693f WebCore::RenderBox::clampToStartAndEndRegions(WebCore::RenderRegion*) const
3   0x113fdb199 WebCore::computeInlineStaticDistance(WebCore::Length&, WebCore::Length&, WebCore::RenderBox const*, WebCore::RenderBoxModelObject const*, WebCore::LayoutUnit, WebCore::RenderRegion*)
4   0x113fd3ffa WebCore::RenderBox::computePositionedLogicalWidth(WebCore::RenderBox::LogicalExtentComputedValues&, WebCore::RenderRegion*) const
5   0x113fd3176 WebCore::RenderBox::computeLogicalWidthInRegion(WebCore::RenderBox::LogicalExtentComputedValues&, WebCore::RenderRegion*) const
6   0x113fc72f2 WebCore::RenderBox::renderBoxRegionInfo(WebCore::RenderRegion*, WebCore::RenderBox::RenderBoxRegionInfoFlags) const
7   0x113fc732e WebCore::RenderBox::renderBoxRegionInfo(WebCore::RenderRegion*, WebCore::RenderBox::RenderBoxRegionInfoFlags) const
8   0x113fc6e89 WebCore::RenderBox::borderBoxRectInRegion(WebCore::RenderRegion*, WebCore::RenderBox::RenderBoxRegionInfoFlags) const
9   0x1141668bc WebCore::RenderRegion::layoutOverflowRectForBoxForPropagation(WebCore::RenderBox const*)
10  0x1140458bf WebCore::RenderFlowThread::addRegionsOverflowFromChild(WebCore::RenderBox const*, WebCore::RenderBox const*, WebCore::LayoutSize const&)
11  0x113fdfff6 WebCore::RenderBox::addOverflowFromChild(WebCore::RenderBox*, WebCore::LayoutSize const&)
12  0x113f73601 WebCore::RenderBox::addOverflowFromChild(WebCore::RenderBox*)
13  0x113f5f165 WebCore::RenderBlock::addOverflowFromBlockChildren()
14  0x113f5f07a WebCore::RenderBlock::addOverflowFromChildren()
15  0x113f5f1ed WebCore::RenderBlock::computeOverflow(WebCore::LayoutUnit, bool)
16  0x114035783 WebCore::RenderFlexibleBox::layoutBlock(bool, WebCore::LayoutUnit)
17  0x113f5edad WebCore::RenderBlock::layout()
18  0x1141239b3 WebCore::RenderMathMLRow::layout()
19  0x114123446 WebCore::RenderMathMLRow::layout()
20  0x1130a58dc WebCore::RenderElement::layoutIfNeeded()
21  0x113fb8e3f WebCore::RenderBlockFlow::layoutLineBoxes(bool, WebCore::LayoutUnit&, WebCore::LayoutUnit&)
22  0x113f94823 WebCore::RenderBlockFlow::layoutInlineChildren(bool, WebCore::LayoutUnit&, WebCore::LayoutUnit&)
23  0x113f9380a WebCore::RenderBlockFlow::layoutBlock(bool, WebCore::LayoutUnit)
24  0x113f5edad WebCore::RenderBlock::layout()
25  0x11403f72b WebCore::RenderFlowThread::layout()
26  0x11412de25 WebCore::RenderMultiColumnFlowThread::layout()
27  0x113fa750f WebCore::RenderBlockFlow::layoutSpecialExcludedChild(bool)
28  0x113f9494f WebCore::RenderBlockFlow::layoutBlockChildren(bool, WebCore::LayoutUnit&)
29  0x113f9382d WebCore::RenderBlockFlow::layoutBlock(bool, WebCore::LayoutUnit)
30  0x113f5edad WebCore::RenderBlock::layout()
31  0x113f9711c WebCore::RenderBlockFlow::layoutBlockChild(WebCore::RenderBox&, WebCore::RenderBlockFlow::MarginInfo&, WebCore::LayoutUnit&, WebCore::LayoutUnit&)

<rdar://problem/18143573>

[Frédéric Wang (:fredw)]

Is it still a problem?

(I also wonder whether it will disappear after the MathML refactoring)

[Frédéric Wang (:fredw)]

The testcase does not exhibit any crash for me on trunk. Also, after https://trac.webkit.org/wiki/MathML/Early_2016_Refactoring#Phase1 MathML is no longer implemented with flexbox (so WebCore::RenderFlexibleBox::layoutBlock won't be called) and is much stricter with invalid markup (as in the testcase). So I'm resolving this as FIXED.