1273414 - CPUUsage b38.085 firefox.exe!xul.dll!nsCSSBorderRenderer::DrawBorderSidesCompositeColors

Status: RESOLVED DUPLICATE of bug 1269351

(Core :: CSS Parsing and Computation, defect)

Description

[SkyLined]

Attachment: repro.html

Repro:

<progress style=border-left-width:999999999em>

Causes excessive CPU usage in nsCSSBorderRenderer::DrawBorderSidesCompositeColors:
https://mxr.mozilla.org/mozilla-central/source/layout/base/nsCSSRenderingBorders.cpp#723

697   for (uint32_t i = 0; i < uint32_t(maxBorderWidth); i++) {
... lots of computations here...
726   }

maxBorderWidth is controlled through the CSS style. The repro provides a high value that makes this loop take a very long time to complete.

Even if the code inside the loop could be optimized, simply counting up to the highest possible unsigned integer would consume excessive CPU and take a long time.

Possible solutions: a sane limit to the number of loops could be applied, but since the time spent running this loop relies on both the number of loops and the time it takes to complete one loop (which depends on the speed of the machine it is running on), measuring the time spend in the loop and terminating it after a set amount would be a better, but more (if not overly) complex solution.

Comment 1

[SkyLined]

Attachment: BugId report

BugId (https://github.com/SkyLined/BugId) can now detect excessive CPU usage, determine which function is causing it and provide a unique id for the instance.