Lots of drivers do dma to pinned down pages. This cow problem should be pervasive, and could have resulted in many corruption related bugs. Since the driver lost the connection to the parent page, the driver is now copying data into the child's page. Loss of data to the parent can be looked at as a corruption bug.
I ran into this problem with the 2.4 kernel. I would think that this problem is quite widespread. However, since this bug was not addressed for such a long time, I will have to assume that this is not such a common problem.
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