On Tue, 31 Mar 2015 08:50:46 +0000 Naoya Horiguchi <[email protected]>
wrote:
> We are not safe from calling isolate_huge_page() on a hugepage concurrently,
> which can make the victim hugepage in invalid state and results in BUG_ON().
>
> The root problem of this is that we don't have any information on struct page
> (so easily accessible) about hugepages' activeness. Note that hugepages'
> activeness means just being linked to hstate->hugepage_activelist, which is
> not the same as normal pages' activeness represented by PageActive flag.
>
> Normal pages are isolated by isolate_lru_page() which prechecks PageLRU before
> isolation, so let's do similarly for hugetlb with a new PageHugeActive flag.
>
> Set/ClearPageHugeActive should be called within hugetlb_lock. But
> hugetlb_cow()
> and hugetlb_no_page() don't do this, being justified because in these function
> SetPageHugeActive is called right after the hugepage is allocated and no other
> thread tries to isolate it.
>
> ...
>
> +/*
> + * Page flag to show that the hugepage is "active/in-use" (i.e. being linked
> to
> + * hstate->hugepage_activelist.)
> + *
> + * This function can be called for tail pages, but never returns true for
> them.
> + */
> +int PageHugeActive(struct page *page)
> +{
> + VM_BUG_ON_PAGE(!PageHuge(page), page);
> + return PageHead(page) && PagePrivate(&page[1]);
> +}
This is not a "page flag". It is a regular old C function which tests
for a certain page state. Yes, it kind of pretends to act like a
separate page flag but its use of the peculiar naming convention is
rather misleading.
I mean, if you see
SetPageHugeActive(page);
then you expect that to be doing set_bit(PG_hugeactive, &page->flags)
but that isn't what it does, so the name is misleading.
Agree?
From: Andrew Morton <[email protected]>
Subject: mm-hugetlb-introduce-pagehugeactive-flag-fix
s/PageHugeActive/page_huge_active/, make it return bool
Cc: Naoya Horiguchi <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/hugetlb.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff -puN mm/hugetlb.c~mm-hugetlb-introduce-pagehugeactive-flag-fix mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-introduce-pagehugeactive-flag-fix
+++ a/mm/hugetlb.c
@@ -925,25 +925,25 @@ struct hstate *size_to_hstate(unsigned l
}
/*
- * Page flag to show that the hugepage is "active/in-use" (i.e. being linked to
- * hstate->hugepage_activelist.)
+ * Test to determine whether the hugepage is "active/in-use" (i.e. being linked
+ * to hstate->hugepage_activelist.)
*
* This function can be called for tail pages, but never returns true for them.
*/
-int PageHugeActive(struct page *page)
+bool page_huge_active(struct page *page)
{
VM_BUG_ON_PAGE(!PageHuge(page), page);
return PageHead(page) && PagePrivate(&page[1]);
}
/* never called for tail page */
-void SetPageHugeActive(struct page *page)
+void set_page_huge_active(struct page *page)
{
VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
SetPagePrivate(&page[1]);
}
-void ClearPageHugeActive(struct page *page)
+void clear_page_huge_active(struct page *page)
{
VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
ClearPagePrivate(&page[1]);
@@ -977,7 +977,7 @@ void free_huge_page(struct page *page)
restore_reserve = true;
spin_lock(&hugetlb_lock);
- ClearPageHugeActive(page);
+ clear_page_huge_active(page);
hugetlb_cgroup_uncharge_page(hstate_index(h),
pages_per_huge_page(h), page);
if (restore_reserve)
@@ -2998,7 +2998,7 @@ retry_avoidcopy:
copy_user_huge_page(new_page, old_page, address, vma,
pages_per_huge_page(h));
__SetPageUptodate(new_page);
- SetPageHugeActive(new_page);
+ set_page_huge_active(new_page);
mmun_start = address & huge_page_mask(h);
mmun_end = mmun_start + huge_page_size(h);
@@ -3111,7 +3111,7 @@ retry:
}
clear_huge_page(page, address, pages_per_huge_page(h));
__SetPageUptodate(page);
- SetPageHugeActive(page);
+ set_page_huge_active(page);
if (vma->vm_flags & VM_MAYSHARE) {
int err;
@@ -3946,11 +3946,11 @@ bool isolate_huge_page(struct page *page
VM_BUG_ON_PAGE(!PageHead(page), page);
spin_lock(&hugetlb_lock);
- if (!PageHugeActive(page) || !get_page_unless_zero(page)) {
+ if (!page_huge_active(page) || !get_page_unless_zero(page)) {
ret = false;
goto unlock;
}
- ClearPageHugeActive(page);
+ clear_page_huge_active(page);
list_move_tail(&page->lru, list);
unlock:
spin_unlock(&hugetlb_lock);
@@ -3961,7 +3961,7 @@ void putback_active_hugepage(struct page
{
VM_BUG_ON_PAGE(!PageHead(page), page);
spin_lock(&hugetlb_lock);
- SetPageHugeActive(page);
+ set_page_huge_active(page);
list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
spin_unlock(&hugetlb_lock);
put_page(page);
--
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