From: Andrea Arcangeli Date: Mon, 8 Oct 2012 23:33:27 +0000 (-0700) Subject: mm: thp: fix pmd_present for split_huge_page and PROT_NONE with THP X-Git-Tag: v3.7-rc1~74^2~28 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=027ef6c87853b0a9df53175063028edb4950d476;p=pandora-kernel.git mm: thp: fix pmd_present for split_huge_page and PROT_NONE with THP In many places !pmd_present has been converted to pmd_none. For pmds that's equivalent and pmd_none is quicker so using pmd_none is better. However (unless we delete pmd_present) we should provide an accurate pmd_present too. This will avoid the risk of code thinking the pmd is non present because it's under __split_huge_page_map, see the pmd_mknotpresent there and the comment above it. If the page has been mprotected as PROT_NONE, it would also lead to a pmd_present false negative in the same way as the race with split_huge_page. Because the PSE bit stays on at all times (both during split_huge_page and when the _PAGE_PROTNONE bit get set), we could only check for the PSE bit, but checking the PROTNONE bit too is still good to remember pmd_present must always keep PROT_NONE into account. This explains a not reproducible BUG_ON that was seldom reported on the lists. The same issue is in pmd_large, it would go wrong with both PROT_NONE and if it races with split_huge_page. Signed-off-by: Andrea Arcangeli Acked-by: Rik van Riel Cc: Johannes Weiner Cc: Hugh Dickins Cc: Mel Gorman Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed