7 files changed, 106 insertions, 47 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f99a099a7747..1375494c8cb6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -872,7 +872,7 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 
 #ifdef CONFIG_MIGRATION
 static int btree_migratepage(struct address_space *mapping,
-                        struct page *newpage, struct page *page)
+                        struct page *newpage, struct page *page, bool sync)
 {
         /*
          * we can't safely write a btree page from here,
@@ -887,7 +887,7 @@ static int btree_migratepage(struct address_space *mapping,
         if (page_has_private(page) &&
             !try_to_release_page(page, GFP_KERNEL))
                 return -EAGAIN;
-        return migrate_page(mapping, newpage, page);
+        return migrate_page(mapping, newpage, page, sync);
 }
 #endif
 
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index e425ad9d0490..06fd4608a990 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -583,7 +583,8 @@ static int hugetlbfs_set_page_dirty(struct page *page)
 }
 
 static int hugetlbfs_migrate_page(struct address_space *mapping,
-                                struct page *newpage, struct page *page)
+                                struct page *newpage, struct page *page,
+                                bool sync)
 {
         int rc;
 
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 5ee92538b063..114398a15830 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -332,7 +332,7 @@ void nfs_commit_release_pages(struct nfs_write_data *data);
 
 #ifdef CONFIG_MIGRATION
 extern int nfs_migrate_page(struct address_space *,
-                struct page *, struct page *);
+                struct page *, struct page *, bool);
 #else
 #define nfs_migrate_page NULL
 #endif
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 0c3885255f97..889e98bc5a21 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1688,7 +1688,7 @@ out_error:
 
 #ifdef CONFIG_MIGRATION
 int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
-                struct page *page)
+                struct page *page, bool sync)
 {
         /*
          * If PagePrivate is set, then the page is currently associated with
@@ -1703,7 +1703,7 @@ int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
 
         nfs_fscache_release_page(page, GFP_KERNEL);
 
-        return migrate_page(mapping, newpage, page);
+        return migrate_page(mapping, newpage, page, sync);
 }
 #endif
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a7409bc157e0..b92b73d0b2b9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -609,9 +609,12 @@ struct address_space_operations {
                         loff_t offset, unsigned long nr_segs);
         int (*get_xip_mem)(struct address_space *, pgoff_t, int,
                                                 void **, unsigned long *);
-        /* migrate the contents of a page to the specified target */
+        /*
+         * migrate the contents of a page to the specified target. If sync
+         * is false, it must not block.
+         */
         int (*migratepage) (struct address_space *,
-                        struct page *, struct page *);
+                        struct page *, struct page *, bool);
         int (*launder_page) (struct page *);
         int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
                                         unsigned long);
@@ -2537,7 +2540,7 @@ extern int generic_check_addressable(unsigned, u64);
 
 #ifdef CONFIG_MIGRATION
 extern int buffer_migrate_page(struct address_space *,
-                                struct page *, struct page *);
+                                struct page *, struct page *, bool);
 #else
 #define buffer_migrate_page NULL
 #endif
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index e39aeecfe9a2..14e6d2a88475 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -11,7 +11,7 @@ typedef struct page *new_page_t(struct page *, unsigned long private, int **);
 
 extern void putback_lru_pages(struct list_head *l);
 extern int migrate_page(struct address_space *,
-                        struct page *, struct page *);
+                        struct page *, struct page *, bool);
 extern int migrate_pages(struct list_head *l, new_page_t x,
                         unsigned long private, bool offlining,
                         bool sync);
diff --git a/mm/migrate.c b/mm/migrate.c
index fc391985899f..4e86f3bacb85 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -216,6 +216,55 @@ out:
         pte_unmap_unlock(ptep, ptl);
 }
 
+#ifdef CONFIG_BLOCK
+/* Returns true if all buffers are successfully locked */
+static bool buffer_migrate_lock_buffers(struct buffer_head *head, bool sync)
+{
+        struct buffer_head *bh = head;
+
+        /* Simple case, sync compaction */
+        if (sync) {
+                do {
+                        get_bh(bh);
+                        lock_buffer(bh);
+                        bh = bh->b_this_page;
+
+                } while (bh != head);
+
+                return true;
+        }
+
+        /* 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;
+                }
+
+                bh = bh->b_this_page;
+        } while (bh != head);
+        return true;
+}
+#else
+static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
+                                                                bool sync)
+{
+        return true;
+}
+#endif /* CONFIG_BLOCK */
+
 /*
  * Replace the page in the mapping.
  *
@@ -225,7 +274,8 @@ out:
  * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
  */
 static int migrate_page_move_mapping(struct address_space *mapping,
-                struct page *newpage, struct page *page)
+                struct page *newpage, struct page *page,
+                struct buffer_head *head, bool sync)
 {
         int expected_count;
         void **pslot;
@@ -255,6 +305,19 @@ static int migrate_page_move_mapping(struct address_space *mapping,
         }
 
         /*
+         * In the async migration case of moving a page with buffers, lock the
+         * buffers using trylock before the mapping is moved. If the mapping
+         * was moved, we later failed to lock the buffers and could not move
+         * the mapping back due to an elevated page count, we would have to
+         * block waiting on other references to be dropped.
+         */
+        if (!sync && head && !buffer_migrate_lock_buffers(head, sync)) {
+                page_unfreeze_refs(page, expected_count);
+                spin_unlock_irq(&mapping->tree_lock);
+                return -EAGAIN;
+        }
+
+        /*
          * Now we know that no one else is looking at the page.
          */
         get_page(newpage);      /* add cache reference */
@@ -409,13 +472,13 @@ EXPORT_SYMBOL(fail_migrate_page);
  * Pages are locked upon entry and exit.
  */
 int migrate_page(struct address_space *mapping,
-                struct page *newpage, struct page *page)
+                struct page *newpage, struct page *page, bool sync)
 {
         int rc;
 
         BUG_ON(PageWriteback(page));    /* Writeback must be complete */
 
-        rc = migrate_page_move_mapping(mapping, newpage, page);
+        rc = migrate_page_move_mapping(mapping, newpage, page, NULL, sync);
 
         if (rc)
                 return rc;
@@ -432,28 +495,28 @@ EXPORT_SYMBOL(migrate_page);
  * exist.
  */
 int buffer_migrate_page(struct address_space *mapping,
-                struct page *newpage, struct page *page)
+                struct page *newpage, struct page *page, bool sync)
 {
         struct buffer_head *bh, *head;
         int rc;
 
         if (!page_has_buffers(page))
-                return migrate_page(mapping, newpage, page);
+                return migrate_page(mapping, newpage, page, sync);
 
         head = page_buffers(page);
 
-        rc = migrate_page_move_mapping(mapping, newpage, page);
+        rc = migrate_page_move_mapping(mapping, newpage, page, head, sync);
 
         if (rc)
                 return rc;
 
-        bh = head;
-        do {
-                get_bh(bh);
-                lock_buffer(bh);
-                bh = bh->b_this_page;
-
-        } while (bh != head);
+        /*
+         * In the async case, migrate_page_move_mapping locked the buffers
+         * with an IRQ-safe spinlock held. In the sync case, the buffers
+         * need to be locked now
+         */
+        if (sync)
+                BUG_ON(!buffer_migrate_lock_buffers(head, sync));
 
         ClearPagePrivate(page);
         set_page_private(newpage, page_private(page));
@@ -530,10 +593,13 @@ static int writeout(struct address_space *mapping, struct page *page)
  * Default handling if a filesystem does not provide a migration function.
  */
 static int fallback_migrate_page(struct address_space *mapping,
-        struct page *newpage, struct page *page)
+        struct page *newpage, struct page *page, bool sync)
 {
-        if (PageDirty(page))
+        if (PageDirty(page)) {
+                if (!sync)
+                        return -EBUSY;
                 return writeout(mapping, page);
+        }
 
         /*
          * Buffers may be managed in a filesystem specific way.
@@ -543,7 +609,7 @@ static int fallback_migrate_page(struct address_space *mapping,
             !try_to_release_page(page, GFP_KERNEL))
                 return -EAGAIN;
 
-        return migrate_page(mapping, newpage, page);
+        return migrate_page(mapping, newpage, page, sync);
 }
 
 /*
@@ -579,29 +645,18 @@ static int move_to_new_page(struct page *newpage, struct page *page,
 
         mapping = page_mapping(page);
         if (!mapping)
-                rc = migrate_page(mapping, newpage, page);
-        else {
+                rc = migrate_page(mapping, newpage, page, sync);
+        else if (mapping->a_ops->migratepage)
                 /*
-                 * Do not writeback pages if !sync and migratepage is
-                 * not pointing to migrate_page() which is nonblocking
-                 * (swapcache/tmpfs uses migratepage = migrate_page).
+                 * Most pages have a mapping and most filesystems provide a
+                 * migratepage callback. Anonymous pages are part of swap
+                 * space which also has its own migratepage callback. This
+                 * is the most common path for page migration.
                  */
-                if (PageDirty(page) && !sync &&
-                    mapping->a_ops->migratepage != migrate_page)
-                        rc = -EBUSY;
-                else if (mapping->a_ops->migratepage)
-                        /*
-                         * Most pages have a mapping and most filesystems
-                         * should provide a migration function. Anonymous
-                         * pages are part of swap space which also has its
-                         * own migration function. This is the most common
-                         * path for page migration.
-                         */
-                        rc = mapping->a_ops->migratepage(mapping,
-                                                        newpage, page);
-                else
-                        rc = fallback_migrate_page(mapping, newpage, page);
-        }
+                rc = mapping->a_ops->migratepage(mapping,
+                                                newpage, page, sync);
+        else
+                rc = fallback_migrate_page(mapping, newpage, page, sync);
 
         if (rc) {
                 newpage->mapping = NULL;