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SubjectRe: [PATCH] huegtlbfs: fix races and page leaks during migration
On Thu, 21 Feb 2019 11:11:06 -0800 Mike Kravetz <mike.kravetz@oracle.com> wrote:

>
> Sorry for the churn. As I find and fix one issue I seem to discover another.
> There is still at least one more issue with private pages when COW comes into
> play. I continue to work that. I wanted to send this patch earlier as it
> is pretty easy to hit the bugs if you try. If you would prefer another
> approach, let me know.
>

No probs, the bug doesn't seem to be causing a lot of bother out there
and it's cc:stable; there's time to get this right ;)

Here's the delta I queued:

--- a/mm/hugetlb.c~huegtlbfs-fix-races-and-page-leaks-during-migration-update
+++ a/mm/hugetlb.c
@@ -3729,6 +3729,7 @@ static vm_fault_t hugetlb_no_page(struct
pte_t new_pte;
spinlock_t *ptl;
unsigned long haddr = address & huge_page_mask(h);
+ bool new_page = false;

/*
* Currently, we are forced to kill the process in the event the
@@ -3790,6 +3791,7 @@ retry:
}
clear_huge_page(page, address, pages_per_huge_page(h));
__SetPageUptodate(page);
+ new_page = true;

if (vma->vm_flags & VM_MAYSHARE) {
int err = huge_add_to_page_cache(page, mapping, idx);
@@ -3861,8 +3863,9 @@ retry:

spin_unlock(ptl);

- /* May already be set if not newly allocated page */
- set_page_huge_active(page);
+ /* Make newly allocated pages active */
+ if (new_page)
+ set_page_huge_active(page);

unlock_page(page);
out:
--- a/mm/migrate.c~huegtlbfs-fix-races-and-page-leaks-during-migration-update
+++ a/mm/migrate.c
@@ -1315,6 +1315,16 @@ static int unmap_and_move_huge_page(new_
lock_page(hpage);
}

+ /*
+ * Check for pages which are in the process of being freed. Without
+ * page_mapping() set, hugetlbfs specific move page routine will not
+ * be called and we could leak usage counts for subpools.
+ */
+ if (page_private(hpage) && !page_mapping(hpage)) {
+ rc = -EBUSY;
+ goto out_unlock;
+ }
+
if (PageAnon(hpage))
anon_vma = page_get_anon_vma(hpage);

@@ -1345,6 +1355,7 @@ put_anon:
put_new_page = NULL;
}

+out_unlock:
unlock_page(hpage);
out:
if (rc != -EAGAIN)
_

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