mm/z3fold.c: reinitialize zhdr structs after migration

z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
However, zhdr contains fields that can't be directly coppied over (ex:
list_head, a circular linked list).  We only need to initialize the
linked lists in new_zhdr, as z3fold_isolate_page() already ensures that
these lists are empty

Additionally it is possible that zhdr->work has been placed in a
workqueue.  In this case we shouldn't migrate the page, as zhdr->work
references zhdr as opposed to new_zhdr.

Link: http://lkml.kernel.org/r/20190716000520.230595-1-henryburns@google.com
Fixes: 1f862989b04ade61d3 ("mm/z3fold.c: support page migration")
Signed-off-by: Henry Burns <henryburns@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Vitaly Vul <vitaly.vul@sony.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Jonathan Adams <jwadams@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 70008a8fed95..6c72b18d8b9c 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1357,12 +1357,22 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
                 z3fold_page_unlock(zhdr);
                 return -EBUSY;
         }
+        if (work_pending(&zhdr->work)) {
+                z3fold_page_unlock(zhdr);
+                return -EAGAIN;
+        }
         new_zhdr = page_address(newpage);
         memcpy(new_zhdr, zhdr, PAGE_SIZE);
         newpage->private = page->private;
         page->private = 0;
         z3fold_page_unlock(zhdr);
         spin_lock_init(&new_zhdr->page_lock);
+        INIT_WORK(&new_zhdr->work, compact_page_work);
+        /*
+         * z3fold_page_isolate() ensures that new_zhdr->buddy is empty,
+         * so we only have to reinitialize it.
+         */
+        INIT_LIST_HEAD(&new_zhdr->buddy);
         new_mapping = page_mapping(page);
         __ClearPageMovable(page);
         ClearPagePrivate(page);