From ddeaab32a89f04b7e2a2df8771583a719c4ac6b7 Mon Sep 17 00:00:00 2001 From: Mike Kravetz Date: Tue, 8 Jan 2019 15:23:36 -0800 Subject: hugetlbfs: revert "use i_mmap_rwsem for more pmd sharing synchronization" This reverts b43a9990055958e70347c56f90ea2ae32c67334c The reverted commit caused issues with migration and poisoning of anon huge pages. The LTP move_pages12 test will cause an "unable to handle kernel NULL pointer" BUG would occur with stack similar to: RIP: 0010:down_write+0x1b/0x40 Call Trace: migrate_pages+0x81f/0xb90 __ia32_compat_sys_migrate_pages+0x190/0x190 do_move_pages_to_node.isra.53.part.54+0x2a/0x50 kernel_move_pages+0x566/0x7b0 __x64_sys_move_pages+0x24/0x30 do_syscall_64+0x5b/0x180 entry_SYSCALL_64_after_hwframe+0x44/0xa9 The purpose of the reverted patch was to fix some long existing races with huge pmd sharing. It used i_mmap_rwsem for this purpose with the idea that this could also be used to address truncate/page fault races with another patch. Further analysis has determined that i_mmap_rwsem can not be used to address all these hugetlbfs synchronization issues. Therefore, revert this patch while working an another approach to the underlying issues. Link: http://lkml.kernel.org/r/20190103235452.29335-2-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz Reported-by: Jan Stancek Cc: Michal Hocko Cc: Hugh Dickins Cc: Naoya Horiguchi Cc: "Aneesh Kumar K . V" Cc: Andrea Arcangeli Cc: "Kirill A . Shutemov" Cc: Davidlohr Bueso Cc: Prakash Sangappa Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/migrate.c | 13 +------------ 1 file changed, 1 insertion(+), 12 deletions(-) (limited to 'mm/migrate.c') diff --git a/mm/migrate.c b/mm/migrate.c index ccf8966caf6f..a16b15090df3 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1324,19 +1324,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, goto put_anon; if (page_mapped(hpage)) { - struct address_space *mapping = page_mapping(hpage); - - /* - * try_to_unmap could potentially call huge_pmd_unshare. - * Because of this, take semaphore in write mode here and - * set TTU_RMAP_LOCKED to let lower levels know we have - * taken the lock. - */ - i_mmap_lock_write(mapping); try_to_unmap(hpage, - TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS| - TTU_RMAP_LOCKED); - i_mmap_unlock_write(mapping); + TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS); page_was_mapped = 1; } -- cgit v1.2.3 From 80409c65e2c6cd1540045ee01fc55e50d95e0983 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 1 Feb 2019 14:20:27 -0800 Subject: mm: migrate: make buffer_migrate_page_norefs() actually succeed Currently, buffer_migrate_page_norefs() was constantly failing because buffer_migrate_lock_buffers() grabbed reference on each buffer. In fact, there's no reason for buffer_migrate_lock_buffers() to grab any buffer references as the page is locked during all our operation and thus nobody can reclaim buffers from the page. So remove grabbing of buffer references which also makes buffer_migrate_page_norefs() succeed. Link: http://lkml.kernel.org/r/20190116131217.7226-1-jack@suse.cz Fixes: 89cb0888ca14 "mm: migrate: provide buffer_migrate_page_norefs()" Signed-off-by: Jan Kara Cc: Sergey Senozhatsky Cc: Pavel Machek Cc: Mel Gorman Cc: Vlastimil Babka Cc: Andrea Arcangeli Cc: David Rientjes Cc: Michal Hocko Cc: Zi Yan Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/migrate.c | 5 ----- 1 file changed, 5 deletions(-) (limited to 'mm/migrate.c') diff --git a/mm/migrate.c b/mm/migrate.c index a16b15090df3..712b231a7376 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -709,7 +709,6 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head, /* Simple case, sync compaction */ if (mode != MIGRATE_ASYNC) { do { - get_bh(bh); lock_buffer(bh); bh = bh->b_this_page; @@ -720,18 +719,15 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head, /* async case, we cannot block on lock_buffer so use trylock_buffer */ do { - get_bh(bh); if (!trylock_buffer(bh)) { /* * We failed to lock the buffer and cannot stall in * async migration. Release the taken locks */ struct buffer_head *failed_bh = bh; - put_bh(failed_bh); bh = head; while (bh != failed_bh) { unlock_buffer(bh); - put_bh(bh); bh = bh->b_this_page; } return false; @@ -818,7 +814,6 @@ unlock_buffers: bh = head; do { unlock_buffer(bh); - put_bh(bh); bh = bh->b_this_page; } while (bh != head); -- cgit v1.2.3 From e0a352fabce61f730341d119fbedf71ffdb8663f Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Fri, 1 Feb 2019 14:21:19 -0800 Subject: mm: migrate: don't rely on __PageMovable() of newpage after unlocking it We had a race in the old balloon compaction code before b1123ea6d3b3 ("mm: balloon: use general non-lru movable page feature") refactored it that became visible after backporting 195a8c43e93d ("virtio-balloon: deflate via a page list") without the refactoring. The bug existed from commit d6d86c0a7f8d ("mm/balloon_compaction: redesign ballooned pages management") till b1123ea6d3b3 ("mm: balloon: use general non-lru movable page feature"). d6d86c0a7f8d ("mm/balloon_compaction: redesign ballooned pages management") was backported to 3.12, so the broken kernels are stable kernels [3.12 - 4.7]. There was a subtle race between dropping the page lock of the newpage in __unmap_and_move() and checking for __is_movable_balloon_page(newpage). Just after dropping this page lock, virtio-balloon could go ahead and deflate the newpage, effectively dequeueing it and clearing PageBalloon, in turn making __is_movable_balloon_page(newpage) fail. This resulted in dropping the reference of the newpage via putback_lru_page(newpage) instead of put_page(newpage), leading to page->lru getting modified and a !LRU page ending up in the LRU lists. With 195a8c43e93d ("virtio-balloon: deflate via a page list") backported, one would suddenly get corrupted lists in release_pages_balloon(): - WARNING: CPU: 13 PID: 6586 at lib/list_debug.c:59 __list_del_entry+0xa1/0xd0 - list_del corruption. prev->next should be ffffe253961090a0, but was dead000000000100 Nowadays this race is no longer possible, but it is hidden behind very ugly handling of __ClearPageMovable() and __PageMovable(). __ClearPageMovable() will not make __PageMovable() fail, only PageMovable(). So the new check (__PageMovable(newpage)) will still hold even after newpage was dequeued by virtio-balloon. If anybody would ever change that special handling, the BUG would be introduced again. So instead, make it explicit and use the information of the original isolated page before migration. This patch can be backported fairly easy to stable kernels (in contrast to the refactoring). Link: http://lkml.kernel.org/r/20190129233217.10747-1-david@redhat.com Fixes: d6d86c0a7f8d ("mm/balloon_compaction: redesign ballooned pages management") Signed-off-by: David Hildenbrand Reported-by: Vratislav Bendel Acked-by: Michal Hocko Acked-by: Rafael Aquini Cc: Mel Gorman Cc: "Kirill A. Shutemov" Cc: Michal Hocko Cc: Naoya Horiguchi Cc: Jan Kara Cc: Andrea Arcangeli Cc: Dominik Brodowski Cc: Matthew Wilcox Cc: Vratislav Bendel Cc: Rafael Aquini Cc: Konstantin Khlebnikov Cc: Minchan Kim Cc: [3.12 - 4.7] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/migrate.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'mm/migrate.c') diff --git a/mm/migrate.c b/mm/migrate.c index 712b231a7376..d4fd680be3b0 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1130,10 +1130,13 @@ out: * If migration is successful, decrease refcount of the newpage * which will not free the page because new page owner increased * refcounter. As well, if it is LRU page, add the page to LRU - * list in here. + * list in here. Use the old state of the isolated source page to + * determine if we migrated a LRU page. newpage was already unlocked + * and possibly modified by its owner - don't rely on the page + * state. */ if (rc == MIGRATEPAGE_SUCCESS) { - if (unlikely(__PageMovable(newpage))) + if (unlikely(!is_lru)) put_page(newpage); else putback_lru_page(newpage); -- cgit v1.2.3