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 086303b9be64..4106264fbc65 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);