To trigger the bug you have to have _just_ the right memory usage, I
suspect. You literally have to have the destination page directory
allocation unmap the _exact_ source page (which has to be clean) for the
bug to hit.

To trigger the bug, I have to run my test program in a "while true;"
loop for an hour or so.

So I suspect the oops only triggers on the machine that the trigger
program was written for.

Your version of the patch saves a goto in the source, but results in an
extra goto in the generated assembly unless the compiler is clever enough
to notice the double test for NULL.

Never mind, that's a micro-optimization, and your version is cleaner.
Let's go with it if Rajesh can verify that it fixes the problem for him.

I will test the patch and report.

Thanks,
Rajesh


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