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>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 086303b..4106264 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -725,7 +725,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 
                cur = btrfs_find_tree_block(root, blocknr, blocksize);
                if (cur)
-                       uptodate = btrfs_buffer_uptodate(cur, gen);
+                       uptodate = btrfs_buffer_uptodate(cur, gen, 0);
                else
                        uptodate = 0;
                if (!cur || !uptodate) {
@@ -1360,7 +1360,12 @@ static noinline int reada_for_balance(struct btrfs_root *root,
                block1 = btrfs_node_blockptr(parent, slot - 1);
                gen = btrfs_node_ptr_generation(parent, slot - 1);
                eb = btrfs_find_tree_block(root, block1, blocksize);
-               if (eb && btrfs_buffer_uptodate(eb, gen))
+               /*
+                * if we get -eagain from btrfs_buffer_uptodate, we
+                * don't want to return eagain here.  That will loop
+                * forever
+                */
+               if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
                        block1 = 0;
                free_extent_buffer(eb);
        }
@@ -1368,7 +1373,7 @@ static noinline int reada_for_balance(struct btrfs_root *root,
                block2 = btrfs_node_blockptr(parent, slot + 1);
                gen = btrfs_node_ptr_generation(parent, slot + 1);
                eb = btrfs_find_tree_block(root, block2, blocksize);
-               if (eb && btrfs_buffer_uptodate(eb, gen))
+               if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
                        block2 = 0;
                free_extent_buffer(eb);
        }
@@ -1506,8 +1511,9 @@ read_block_for_search(struct btrfs_trans_handle *trans,
 
        tmp = btrfs_find_tree_block(root, blocknr, blocksize);
        if (tmp) {
-               if (btrfs_buffer_uptodate(tmp, 0)) {
-                       if (btrfs_buffer_uptodate(tmp, gen)) {
+               /* first we do an atomic uptodate check */
+               if (btrfs_buffer_uptodate(tmp, 0, 1) > 0) {
+                       if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
                                /*
                                 * we found an up to date block without
                                 * sleeping, return
@@ -1525,8 +1531,9 @@ read_block_for_search(struct btrfs_trans_handle *trans,
                        free_extent_buffer(tmp);
                        btrfs_set_path_blocking(p);
 
+                       /* now we're allowed to do a blocking uptodate check */
                        tmp = read_tree_block(root, blocknr, blocksize, gen);
-                       if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
+                       if (tmp && btrfs_buffer_uptodate(tmp, gen, 0) > 0) {
                                *eb_ret = tmp;
                                return 0;
                        }
@@ -1561,7 +1568,7 @@ read_block_for_search(struct btrfs_trans_handle *trans,
                 * and give up so that our caller doesn't loop forever
                 * on our EAGAINs.
                 */
-               if (!btrfs_buffer_uptodate(tmp, 0))
+               if (!btrfs_buffer_uptodate(tmp, 0, 0))
                        ret = -EIO;
                free_extent_buffer(tmp);
        }
@@ -4045,7 +4052,7 @@ again:
                        tmp = btrfs_find_tree_block(root, blockptr,
                                            btrfs_level_size(root, level - 1));
 
-                       if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
+                       if (tmp && btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
                                free_extent_buffer(tmp);
                                break;
                        }
@@ -4168,7 +4175,8 @@ next:
                                struct extent_buffer *cur;
                                cur = btrfs_find_tree_block(root, blockptr,
                                            btrfs_level_size(root, level - 1));
-                               if (!cur || !btrfs_buffer_uptodate(cur, gen)) {
+                               if (!cur ||
+                                   btrfs_buffer_uptodate(cur, gen, 1) <= 0) {
                                        slot++;
                                        if (cur)
                                                free_extent_buffer(cur);

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d0c969b..a7ffc88 100644 (file)
--- 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;
 }
 

diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index a7ace1a..ab1830a 100644 (file)
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -66,7 +66,8 @@ void btrfs_btree_balance_dirty(struct btrfs_root *root, unsigned long nr);
 void __btrfs_btree_balance_dirty(struct btrfs_root *root, unsigned long nr);
 void btrfs_free_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root);
 void btrfs_mark_buffer_dirty(struct extent_buffer *buf);
-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 btrfs_set_buffer_uptodate(struct extent_buffer *buf);
 int btrfs_read_buffer(struct extent_buffer *buf, u64 parent_transid);
 u32 btrfs_csum_data(struct btrfs_root *root, char *data, u32 seed, size_t len);

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 6fc2e6f..49fd7b6 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -6568,7 +6568,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                        goto skip;
        }
 
-       if (!btrfs_buffer_uptodate(next, generation)) {
+       if (!btrfs_buffer_uptodate(next, generation, 0)) {
                btrfs_tree_unlock(next);
                free_extent_buffer(next);
                next = NULL;

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index d017283..eb1ae90 100644 (file)
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -279,7 +279,7 @@ static int process_one_buffer(struct btrfs_root *log,
                                                log->fs_info->extent_root,
                                                eb->start, eb->len);
 
-       if (btrfs_buffer_uptodate(eb, gen)) {
+       if (btrfs_buffer_uptodate(eb, gen, 0)) {
                if (wc->write)
                        btrfs_write_tree_block(eb);
                if (wc->wait)