From: Minchan Kim Date: Mon, 29 Apr 2013 22:08:15 +0000 (-0700) Subject: THP: fix comment about memory barrier X-Git-Tag: omap-for-v3.10/dt-fixes-for-merge-window~128^2~29 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=52f37629fd3c7b24e1e6c125e665454cd7ac1acb;p=pandora-kernel.git THP: fix comment about memory barrier Currently the memory barrier in __do_huge_pmd_anonymous_page doesn't work. Because lru_cache_add_lru uses pagevec so it could miss spinlock easily so above rule was broken so user might see inconsistent data. I was not first person who pointed out the problem. Mel and Peter pointed out a few months ago and Peter pointed out further that even spin_lock/unlock can't make sure of it: http://marc.info/?t=134333512700004 In particular: *A = a; LOCK UNLOCK *B = b; may occur as: LOCK, STORE *B, STORE *A, UNLOCK At last, Hugh pointed out that even we don't need memory barrier in there because __SetPageUpdate already have done it from Nick's commit 0ed361dec369 ("mm: fix PageUptodate data race") explicitly. So this patch fixes comment on THP and adds same comment for do_anonymous_page, too because everybody except Hugh was missing that. It means we need a comment about that. Signed-off-by: Minchan Kim Acked-by: Andrea Arcangeli Acked-by: David Rientjes Acked-by: KAMEZAWA Hiroyuki Cc: Mel Gorman Cc: Hugh Dickins Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed