Btrfs: Use a mutex in the extent buffer for tree block locking

This replaces the use of the page cache lock bit for locking, which wasn't
suitable for block size < page size and couldn't be used recursively.

The mutexes alone don't fix either problem, but they are the first step.

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

4 files changed, 17 insertions, 13 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ccd49322f793..c51cd11de206 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1451,7 +1451,7 @@ static int pin_down_bytes(struct btrfs_root *root, u64 bytenr, u32 num_bytes,
                 struct extent_buffer *buf;
                 buf = btrfs_find_tree_block(root, bytenr, num_bytes);
                 if (buf) {
-                        if (!btrfs_try_tree_lock(buf) &&
+                        if (btrfs_try_tree_lock(buf) &&
                             btrfs_buffer_uptodate(buf, 0)) {
                                 u64 transid =
                                     root->fs_info->running_transaction->transid;
@@ -3345,11 +3345,6 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 set_state_private(block_group_cache, found_key.objectid,
                                   (unsigned long)cache);
 
-                /* hack for now */
-                if (cache->flags & BTRFS_BLOCK_GROUP_METADATA) {
-                        cache_block_group(root->fs_info->extent_root,
-                                          cache);
-                }
                 if (key.objectid >=
                     btrfs_super_total_bytes(&info->super_copy))
                         break;
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 32bb4ed3723d..7380449cb5b3 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2690,6 +2690,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
         eb = kmem_cache_zalloc(extent_buffer_cache, mask);
         eb->start = start;
         eb->len = len;
+        mutex_init(&eb->mutex);
         spin_lock_irqsave(&leak_lock, flags);
         list_add(&eb->leak_list, &buffers);
         spin_unlock_irqrestore(&leak_lock, flags);
@@ -2837,6 +2838,7 @@ int clear_extent_buffer_dirty(struct extent_io_tree *tree,
 
         for (i = 0; i < num_pages; i++) {
                 page = extent_buffer_page(eb, i);
+                lock_page(page);
                 if (i == 0)
                         set_page_extent_head(page, eb->len);
                 else
@@ -2854,6 +2856,7 @@ int clear_extent_buffer_dirty(struct extent_io_tree *tree,
                         end  = start + PAGE_CACHE_SIZE - 1;
                         if (test_range_bit(tree, start, end,
                                            EXTENT_DIRTY, 0)) {
+                                unlock_page(page);
                                 continue;
                         }
                 }
@@ -2865,6 +2868,7 @@ int clear_extent_buffer_dirty(struct extent_io_tree *tree,
                                                 PAGECACHE_TAG_DIRTY);
                 }
                 read_unlock_irq(&page->mapping->tree_lock);
+                unlock_page(page);
         }
         return 0;
 }
@@ -2893,12 +2897,17 @@ int set_extent_buffer_dirty(struct extent_io_tree *tree,
                  * on us if the page isn't already dirty.
                  */
                 if (i == 0) {
+                        lock_page(page);
                         set_page_extent_head(page, eb->len);
                 } else if (PagePrivate(page) &&
                            page->private != EXTENT_PAGE_PRIVATE) {
+                        lock_page(page);
                         set_page_extent_mapped(page);
+                        unlock_page(page);
                 }
                 __set_page_dirty_nobuffers(extent_buffer_page(eb, i));
+                if (i == 0)
+                        unlock_page(page);
         }
         return set_extent_dirty(tree, eb->start,
                                 eb->start + eb->len - 1, GFP_NOFS);
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index dd367617d780..6c03e6a19938 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -90,6 +90,7 @@ struct extent_buffer {
         int flags;
         struct list_head leak_list;
         struct rb_node rb_node;
+        struct mutex mutex;
 };
 
 struct extent_map_tree;
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 058a506a0dd8..01a9ac2be3f7 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -29,32 +29,31 @@ int btrfs_tree_lock(struct extent_buffer *eb)
 {
         int i;
 
-        if (!TestSetPageLocked(eb->first_page))
+        if (mutex_trylock(&eb->mutex))
                 return 0;
         for (i = 0; i < 512; i++) {
                 cpu_relax();
-                if (!TestSetPageLocked(eb->first_page))
+                if (mutex_trylock(&eb->mutex))
                         return 0;
         }
         cpu_relax();
-        lock_page(eb->first_page);
+        mutex_lock(&eb->mutex);
         return 0;
 }
 
 int btrfs_try_tree_lock(struct extent_buffer *eb)
 {
-        return TestSetPageLocked(eb->first_page);
+        return mutex_trylock(&eb->mutex);
 }
 
 int btrfs_tree_unlock(struct extent_buffer *eb)
 {
-        WARN_ON(!PageLocked(eb->first_page));
-        unlock_page(eb->first_page);
+        mutex_unlock(&eb->mutex);
         return 0;
 }
 
 int btrfs_tree_locked(struct extent_buffer *eb)
 {
-        return PageLocked(eb->first_page);
+        return mutex_is_locked(&eb->mutex);
 }