install_page() lockup

[Andrew Morton <akpm@digeo.com>]

I'm getting lockups in install_page() with shared pagetables
enabled.  I haven't really delved into it.  It happens under
heavy memory pressure on SMP.

Ingo's new patch is using install_page much more than we
used to (I don't think I've ever run it before), so we're
running fairly untested codepaths here.

I tried this:

 mm/fremap.c |    2 ++
 1 files changed, 2 insertions(+)

--- 25/mm/fremap.c~a	Tue Oct 22 22:08:26 2002
+++ 25-akpm/mm/fremap.c	Tue Oct 22 22:09:02 2002
@@ -72,7 +72,9 @@ int install_page(struct mm_struct *mm, s
 		pte_page_lock(ptepage);
 		if (page_count(ptepage) > 1) {
 			pte = pte_unshare(mm, pmd, addr);
+			pte_page_unlock(ptepage);
 			ptepage = pmd_page(*pmd);
+			pte_page_lock(ptepage);
 		} else
 			pte = pte_offset_map(pmd, addr);
 	} else {

.

Because doing a pte_page_lock(ptepage) and then losing
track of the page we just locked looks fishy.  Didn't
help though.

Dave could you please review the code in there?  It's probably
something simple.

Thanks.
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