Patch "mm: fix swapoff hang after page migration and fork" has been added to the 3.17-stable tree

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This is a note to let you know that I've just added the patch titled

    mm: fix swapoff hang after page migration and fork

to the 3.17-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-fix-swapoff-hang-after-page-migration-and-fork.patch
and it can be found in the queue-3.17 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 2022b4d18a491a578218ce7a4eca8666db895a73 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@xxxxxxxxxx>
Date: Tue, 2 Dec 2014 15:59:39 -0800
Subject: mm: fix swapoff hang after page migration and fork

From: Hugh Dickins <hughd@xxxxxxxxxx>

commit 2022b4d18a491a578218ce7a4eca8666db895a73 upstream.

I've been seeing swapoff hangs in recent testing: it's cycling around
trying unsuccessfully to find an mm for some remaining pages of swap.

I have been exercising swap and page migration more heavily recently,
and now notice a long-standing error in copy_one_pte(): it's trying to
add dst_mm to swapoff's mmlist when it finds a swap entry, but is doing
so even when it's a migration entry or an hwpoison entry.

Which wouldn't matter much, except it adds dst_mm next to src_mm,
assuming src_mm is already on the mmlist: which may not be so.  Then if
pages are later swapped out from dst_mm, swapoff won't be able to find
where to replace them.

There's already a !non_swap_entry() test for stats: move that up before
the swap_duplicate() and the addition to mmlist.

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kelley Nielsen <kelleynnn@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/memory.c |   24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -815,20 +815,20 @@ copy_one_pte(struct mm_struct *dst_mm, s
 		if (!pte_file(pte)) {
 			swp_entry_t entry = pte_to_swp_entry(pte);
 
-			if (swap_duplicate(entry) < 0)
-				return entry.val;
+			if (likely(!non_swap_entry(entry))) {
+				if (swap_duplicate(entry) < 0)
+					return entry.val;
 
-			/* make sure dst_mm is on swapoff's mmlist. */
-			if (unlikely(list_empty(&dst_mm->mmlist))) {
-				spin_lock(&mmlist_lock);
-				if (list_empty(&dst_mm->mmlist))
-					list_add(&dst_mm->mmlist,
-						 &src_mm->mmlist);
-				spin_unlock(&mmlist_lock);
-			}
-			if (likely(!non_swap_entry(entry)))
+				/* make sure dst_mm is on swapoff's mmlist. */
+				if (unlikely(list_empty(&dst_mm->mmlist))) {
+					spin_lock(&mmlist_lock);
+					if (list_empty(&dst_mm->mmlist))
+						list_add(&dst_mm->mmlist,
+							 &src_mm->mmlist);
+					spin_unlock(&mmlist_lock);
+				}
 				rss[MM_SWAPENTS]++;
-			else if (is_migration_entry(entry)) {
+			} else if (is_migration_entry(entry)) {
 				page = migration_entry_to_page(entry);
 
 				if (PageAnon(page))


Patches currently in stable-queue which might be from hughd@xxxxxxxxxx are

queue-3.17/mm-fix-swapoff-hang-after-page-migration-and-fork.patch
queue-3.17/mm-fix-anon_vma_clone-error-treatment.patch
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