Commit 2022b4d1 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds

mm: fix swapoff hang after page migration and fork

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: default avatarHugh Dickins <hughd@google.com>
Cc: Kelley Nielsen <kelleynnn@gmail.com>
Cc: <stable@vger.kernel.org>	[2.6.18+]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1ead0e79
...@@ -815,20 +815,20 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, ...@@ -815,20 +815,20 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
if (!pte_file(pte)) { if (!pte_file(pte)) {
swp_entry_t entry = pte_to_swp_entry(pte); swp_entry_t entry = pte_to_swp_entry(pte);
if (swap_duplicate(entry) < 0) if (likely(!non_swap_entry(entry))) {
return entry.val; if (swap_duplicate(entry) < 0)
return entry.val;
/* make sure dst_mm is on swapoff's mmlist. */
if (unlikely(list_empty(&dst_mm->mmlist))) { /* make sure dst_mm is on swapoff's mmlist. */
spin_lock(&mmlist_lock); if (unlikely(list_empty(&dst_mm->mmlist))) {
if (list_empty(&dst_mm->mmlist)) spin_lock(&mmlist_lock);
list_add(&dst_mm->mmlist, if (list_empty(&dst_mm->mmlist))
&src_mm->mmlist); list_add(&dst_mm->mmlist,
spin_unlock(&mmlist_lock); &src_mm->mmlist);
} spin_unlock(&mmlist_lock);
if (likely(!non_swap_entry(entry))) }
rss[MM_SWAPENTS]++; rss[MM_SWAPENTS]++;
else if (is_migration_entry(entry)) { } else if (is_migration_entry(entry)) {
page = migration_entry_to_page(entry); page = migration_entry_to_page(entry);
if (PageAnon(page)) if (PageAnon(page))
......
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