diff options
| author | Hugh Dickins <hugh@veritas.com> | 2008-03-04 14:29:06 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-03-04 16:35:14 -0800 |
| commit | 98837c7f82ef78aa38f40462aa2fcac68fd3acbf (patch) | |
| tree | 6d76841b18b57a9202d7699ba4dca5b39fdd7aea /mm | |
| parent | 61469f1d51777fc3b6d8d70da8373ee77ee13349 (diff) | |
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>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/migrate.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/mm/migrate.c b/mm/migrate.c index a73504ff5ab..4e0eccca5e2 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -153,11 +153,6 @@ static void remove_migration_pte(struct vm_area_struct *vma, return; } - if (mem_cgroup_charge(new, mm, GFP_KERNEL)) { - pte_unmap(ptep); - return; - } - ptl = pte_lockptr(mm, pmd); spin_lock(ptl); pte = *ptep; @@ -169,6 +164,20 @@ static void remove_migration_pte(struct vm_area_struct *vma, if (!is_migration_entry(entry) || migration_entry_to_page(entry) != old) goto out; + /* + * Yes, ignore the return value from a GFP_ATOMIC mem_cgroup_charge. + * Failure is not an option here: we're now expected to remove every + * migration pte, and will cause crashes otherwise. Normally this + * is not an issue: mem_cgroup_prepare_migration bumped up the old + * page_cgroup count for safety, that's now attached to the new page, + * so this charge should just be another incrementation of the count, + * to keep in balance with rmap.c's mem_cgroup_uncharging. But if + * there's been a force_empty, those reference counts may no longer + * be reliable, and this charge can actually fail: oh well, we don't + * make the situation any worse by proceeding as if it had succeeded. + */ + mem_cgroup_charge(new, mm, GFP_ATOMIC); + get_page(new); pte = pte_mkold(mk_pte(new, vma->vm_page_prot)); if (is_write_migration_entry(entry)) |