From: Mel Gorman Date: Mon, 24 May 2010 21:32:19 +0000 (-0700) Subject: mm: migration: do not try to migrate unmapped anonymous pages X-Git-Tag: v2.6.35-rc1~382 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=67b9509b2c68ae38cecb83a239881cb0ddf087dc;p=pandora-kernel.git mm: migration: do not try to migrate unmapped anonymous pages rmap_walk_anon() was triggering errors in memory compaction that look like use-after-free errors. The problem is that between the page being isolated from the LRU and rcu_read_lock() being taken, the mapcount of the page dropped to 0 and the anon_vma gets freed. This can happen during memory compaction if pages being migrated belong to a process that exits before migration completes. Hence, the use-after-free race looks like 1. Page isolated for migration 2. Process exits 3. page_mapcount(page) drops to zero so anon_vma was no longer reliable 4. unmap_and_move() takes the rcu_lock but the anon_vma is already garbage 4. call try_to_unmap, looks up tha anon_vma and "locks" it but the lock is garbage. This patch checks the mapcount after the rcu lock is taken. If the mapcount is zero, the anon_vma is assumed to be freed and no further action is taken. Signed-off-by: Mel Gorman Acked-by: Rik van Riel Reviewed-by: Minchan Kim Reviewed-by: KAMEZAWA Hiroyuki Cc: KOSAKI Motohiro Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed