Hi,

quoted

quoted

However, if we're on an unlikely error path or
similar and other options aren't suitable...

Maintaining atomicity in uniprocessor systems is easy
by preempt_enable and preempt_disable during the
operation. This implementation cannot be used for SMP
systems. 
Now during the time a page is copied/updatede if a
page is accessed the copied contents become invalid,
as updation is not done. Also during updation a
similar situation might arise.
The problem we are facing is to maintain the atomicity
of this operation on SMP boxes.

I think what you really want to do is keep anybody else from making a
new pte to the page, once you've invalidated all of the existing ones,
right?

Holding a lock_page() should do the trick.  Anybody that goes any pulls
the page out of the page cache has to do a lock_page() and check
page->mapping before they can establish a pte to it, so you can stop
that.  Since you're invalidating page->mapping before you move the page
(you *are* doing this, right?), it will end up working itself out.  

We should know that many part of kernel code will access the page
without holding a lock_page(). The lock_page() can't block them.

Thank you,
Hirokazu Takahashi.
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