Btrfs: avoid sleeping in verify_parent_transid while atomic

verify_parent_transid needs to lock the extent range to make
sure no IO is underway, and so it can safely clear the
uptodate bits if our checks fail.

But, a few callers are using it with spinlocks held.  Most
of the time, the generation numbers are going to match, and
we don't want to switch to a blocking lock just for the error
case.  This adds an atomic flag to verify_parent_transid,
and changes it to return EAGAIN if it needs to block to
properly verifiy things.

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

1 files changed, 13 insertions, 5 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d0c969beaad4..a7ffc88a7dbe 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -323,7 +323,8 @@ static int csum_tree_block(struct btrfs_root *root, struct extent_buffer *buf,
  * in the wrong place.
  */
 static int verify_parent_transid(struct extent_io_tree *io_tree,
-                                 struct extent_buffer *eb, u64 parent_transid)
+                                 struct extent_buffer *eb, u64 parent_transid,
+                                 int atomic)
 {
         struct extent_state *cached_state = NULL;
         int ret;
@@ -331,6 +332,9 @@ static int verify_parent_transid(struct extent_io_tree *io_tree,
         if (!parent_transid || btrfs_header_generation(eb) == parent_transid)
                 return 0;
 
+        if (atomic)
+                return -EAGAIN;
+
         lock_extent_bits(io_tree, eb->start, eb->start + eb->len - 1,
                          0, &cached_state);
         if (extent_buffer_uptodate(eb) &&
@@ -372,7 +376,8 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
                 ret = read_extent_buffer_pages(io_tree, eb, start,
                                                WAIT_COMPLETE,
                                                btree_get_extent, mirror_num);
-                if (!ret && !verify_parent_transid(io_tree, eb, parent_transid))
+                if (!ret && !verify_parent_transid(io_tree, eb,
+                                                   parent_transid, 0))
                         break;
 
                 /*
@@ -1202,7 +1207,7 @@ static int __must_check find_and_setup_root(struct btrfs_root *tree_root,
         root->commit_root = NULL;
         root->node = read_tree_block(root, btrfs_root_bytenr(&root->root_item),
                                      blocksize, generation);
-        if (!root->node || !btrfs_buffer_uptodate(root->node, generation)) {
+        if (!root->node || !btrfs_buffer_uptodate(root->node, generation, 0)) {
                 free_extent_buffer(root->node);
                 root->node = NULL;
                 return -EIO;
@@ -3143,7 +3148,8 @@ int close_ctree(struct btrfs_root *root)
         return 0;
 }
 
-int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid)
+int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,
+                          int atomic)
 {
         int ret;
         struct inode *btree_inode = buf->pages[0]->mapping->host;
@@ -3153,7 +3159,9 @@ int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid)
                 return ret;
 
         ret = verify_parent_transid(&BTRFS_I(btree_inode)->io_tree, buf,
-                                    parent_transid);
+                                    parent_transid, atomic);
+        if (ret == -EAGAIN)
+                return ret;
         return !ret;
 }