Hi Andrew,
On Wed, Dec 18, 2013 at 04:28:58PM -0800, Andrew Morton wrote:
>On Thu, 19 Dec 2013 08:16:35 +0800 Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> wrote:
>
>> page_get_anon_vma() called in page_referenced_anon() will lock and
>> increase the refcount of anon_vma, page won't be locked for anonymous
>> page. This patch fix it by skip check anonymous page locked.
>>
>> [ 588.698828] kernel BUG at mm/rmap.c:1663!
>
>Why is all this suddenly happening. Did we change something, or did a
>new test get added to trinity?
>
They are introduced by Joonsoo's rmap_walk.
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1660,7 +1660,8 @@ done:
>>
>> int rmap_walk(struct page *page, struct rmap_walk_control *rwc)
>> {
>> - VM_BUG_ON(!PageLocked(page));
>> + if (!PageAnon(page) || PageKsm(page))
>> + VM_BUG_ON(!PageLocked(page));
>>
>> if (unlikely(PageKsm(page)))
>> return rmap_walk_ksm(page, rwc);
>
>Is there any reason why rmap_walk_ksm() and rmap_walk_file() *need*
>PageLocked() whereas rmap_walk_anon() does not? If so, let's implement
>it like this:
All callsites of rmap_walk()
try_to_unmap() page should be lockecd (checked in rmap_walk())
try_to_munlock() pages should be locked (checked in try_to_munlock())
page_referenced() pages should be locked except anonymous page (checked in rmap_walk())
page_mkclean() pages should be locked (checked in page_mkclean())
remove_migration_ptes() pages should be locked (checked in rmap_walk())
We can move PageLocked(page) check to the callsites instead of in
rmap_walk() since anonymous page is not locked in page_referenced().
Regards,
Wanpeng Li
>
>
>--- a/mm/rmap.c~a
>+++ a/mm/rmap.c
>@@ -1716,6 +1716,10 @@ static int rmap_walk_file(struct page *p
> struct vm_area_struct *vma;
> int ret = SWAP_AGAIN;
>
>+ /*
>+ * page must be locked because <reason goes here>
>+ */
>+ VM_BUG_ON(!PageLocked(page));
> if (!mapping)
> return ret;
> mutex_lock(&mapping->i_mmap_mutex);
>@@ -1737,8 +1741,6 @@ static int rmap_walk_file(struct page *p
> int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
> struct vm_area_struct *, unsigned long, void *), void *arg)
> {
>- VM_BUG_ON(!PageLocked(page));
>-
> if (unlikely(PageKsm(page)))
> return rmap_walk_ksm(page, rmap_one, arg);
> else if (PageAnon(page))
>--- a/mm/ksm.c~a
>+++ a/mm/ksm.c
>@@ -2006,6 +2006,9 @@ int rmap_walk_ksm(struct page *page, int
> int search_new_forks = 0;
>
> VM_BUG_ON(!PageKsm(page));
>+ /*
>+ * page must be locked because <reason goes here>
>+ */
> VM_BUG_ON(!PageLocked(page));
>
> stable_node = page_stable_node(page);
>
>
>Or if there is no reason why the page must be locked for
>rmap_walk_ksm() and rmap_walk_file(), let's just remove rmap_walk()'s
>VM_BUG_ON()? And rmap_walk_ksm()'s as well - it's duplicative anyway.
>
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