Re: [PATCH] huegtlbfs: fix races and page leaks during migration

[Andrew Morton <akpm@linux-foundation.org>]

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)
_