quoted

This saves a goto.   It works, but I wasn't able to trigger
the oops without it either.

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.

A minor point. It is not necessary for the src to be clean because a
parallel truncate can also invalidate the src. Actually, my test program
uses truncate to invalidate the src.

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.

Yeah. Andrew's patch is lot cleaner than my _crap_ patch.

Let's go with it if Rajesh can verify that it fixes the problem for him.

Yeap. Andrew's patch fixes the problem. I did put in a printk along with
Andrew's patch to check whether the NULL src condition repeats. I could
trigger the condition again, and the machine didn't oops because of the
patch.

Thanks,
Rajesh


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