From: Hugh Dickins <[email protected]> Subject: 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: Hugh Dickins <[email protected]> Cc: Kelley Nielsen <[email protected]> Cc: <[email protected]> [2.6.18+] Signed-off-by: Andrew Morton <[email protected]> --- mm/memory.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff -puN mm/memory.c~mm-fix-swapoff-hang-after-page-migration-and-fork mm/memory.c --- a/mm/memory.c~mm-fix-swapoff-hang-after-page-migration-and-fork +++ a/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)) _ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
