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, 17 insertions, 9 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 086303b9be6..4106264fbc6 100644
--- 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);