tree 6d76841b18b57a9202d7699ba4dca5b39fdd7aea
parent 61469f1d51777fc3b6d8d70da8373ee77ee13349
author Hugh Dickins <hugh@veritas.com> 1204669746 -0800
committer Linus Torvalds <torvalds@woody.linux-foundation.org> 1204677314 -0800

memcg: fix VM_BUG_ON from page migration

Page migration gave me free_hot_cold_page's VM_BUG_ON page->page_cgroup.
remove_migration_pte was calling mem_cgroup_charge on the new page whenever it
found a swap pte, before it had determined it to be a migration entry.  That
left a surplus reference count on the page_cgroup, so it was still attached
when the page was later freed.

Move that mem_cgroup_charge down to where we're sure it's a migration entry.
We were already under i_mmap_lock or anon_vma->lock, so its GFP_KERNEL was
already inappropriate: change that to GFP_ATOMIC.

It's essential that remove_migration_pte removes all the migration entries,
other crashes follow if not.  So proceed even when the charge fails: normally
it cannot, but after a mem_cgroup_force_empty it might - comment in the code.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>