Btrfs: make sure to flush queued bios if write_cache_pages waits

write_cache_pages tries to build up a large bio to stuff down the pipe.
But if it needs to wait for a page lock, it needs to make sure and send
down any pending writes so we don't deadlock with anyone who has the
page lock and is waiting for writeback of things inside the bio.

Dave Sterba triggered this as a deadlock between the autodefrag code and
the extent write_cache_pages

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 51372a52116703a667bcc0a3646b848ea0b8f0b9..6f58911ece0d9b6c45bca01c869f58f9a6e849e6 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2735,7 +2735,8 @@ int btrfs_read_buffer(struct extent_buffer *buf, u64 parent_transid)
        return ret;
 }
 
-int btree_lock_page_hook(struct page *page)
+static int btree_lock_page_hook(struct page *page, void *data,
+                               void (*flush_fn)(void *))
 {
        struct inode *inode = page->mapping->host;
        struct btrfs_root *root = BTRFS_I(inode)->root;
@@ -2752,7 +2753,10 @@ int btree_lock_page_hook(struct page *page)
        if (!eb)
                goto out;
 
-       btrfs_tree_lock(eb);
+       if (!btrfs_try_tree_write_lock(eb)) {
+               flush_fn(data);
+               btrfs_tree_lock(eb);
+       }
        btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
 
        if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
@@ -2767,7 +2771,10 @@ int btree_lock_page_hook(struct page *page)
        btrfs_tree_unlock(eb);
        free_extent_buffer(eb);
 out:
-       lock_page(page);
+       if (!trylock_page(page)) {
+               flush_fn(data);
+               lock_page(page);
+       }
        return 0;
 }
 

diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index bec3ea4bd67fd465a8a5e008fcae1e7353f573ad..e678539c8519cf4eb081569225de648152d6a712 100644 (file)
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -83,8 +83,6 @@ int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
                             struct btrfs_fs_info *fs_info);
 int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root);
-int btree_lock_page_hook(struct page *page);
-
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 void btrfs_init_lockdep(void);

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f284d4e5f447e10e4a2d662010d43fd7670be9df..b40ba75f4483d205afb08265ddb4e6789f065404 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2613,10 +2613,16 @@ retry:
                         * swizzled back from swapper_space to tmpfs file
                         * mapping
                         */
-                       if (tree->ops && tree->ops->write_cache_pages_lock_hook)
-                               tree->ops->write_cache_pages_lock_hook(page);
-                       else
-                               lock_page(page);
+                       if (tree->ops &&
+                           tree->ops->write_cache_pages_lock_hook) {
+                               tree->ops->write_cache_pages_lock_hook(page,
+                                                              data, flush_fn);
+                       } else {
+                               if (!trylock_page(page)) {
+                                       flush_fn(data);
+                                       lock_page(page);
+                               }
+                       }
 
                        if (unlikely(page->mapping != mapping)) {
                                unlock_page(page);

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 325a346369da041bed0a8633d857a0f942d84875..cbd4824a7c9429ed16bfd8cb0985216ee0e5aae5 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -86,7 +86,8 @@ struct extent_io_ops {
                                  struct extent_state *other);
        void (*split_extent_hook)(struct inode *inode,
                                  struct extent_state *orig, u64 split);
-       int (*write_cache_pages_lock_hook)(struct page *page);
+       int (*write_cache_pages_lock_hook)(struct page *page, void *data,
+                                          void (*flush_fn)(void *));
 };
 
 struct extent_io_tree {