Btrfs: fix race in sync and freeze again

I screwed this up, there is a race between checking if there is a running
transaction and actually starting a transaction in sync where we could race
with a freezer and get ourselves into trouble.  To fix this we need to make
a new join type to only do the try lock on the freeze stuff.  If it fails
we'll return EPERM and just return from sync.  This fixes a hang Liu Bo
reported when running xfstest 68 in a loop.  Thanks,

Reported-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 867e8e799dea84a7e7d7ed85ea0fffc00c7c95d1..903ab2d7068aeac8a06d27a600812234dbfec697 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -854,16 +854,13 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
 
        btrfs_wait_ordered_extents(root, 0, 0);
 
-       spin_lock(&fs_info->trans_lock);
-       if (!fs_info->running_transaction) {
-               spin_unlock(&fs_info->trans_lock);
-               return 0;
-       }
-       spin_unlock(&fs_info->trans_lock);
-
-       trans = btrfs_join_transaction(root);
-       if (IS_ERR(trans))
+       trans = btrfs_join_transaction_freeze(root);
+       if (IS_ERR(trans)) {
+               /* Frozen, don't bother */
+               if (PTR_ERR(trans) == -EPERM)
+                       return 0;
                return PTR_ERR(trans);
+       }
        return btrfs_commit_transaction(trans, root);
 }
 

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c01dec70c960e1c2a213feb422c4660a1b3078a8..e4bfac8d54b8827800fde80cfe84ba94ed96060a 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -272,6 +272,7 @@ enum btrfs_trans_type {
        TRANS_JOIN,
        TRANS_USERSPACE,
        TRANS_JOIN_NOLOCK,
+       TRANS_JOIN_FREEZE,
 };
 
 static int may_wait_transaction(struct btrfs_root *root, int type)
@@ -341,7 +342,11 @@ again:
        if (!h)
                return ERR_PTR(-ENOMEM);
 
-       sb_start_intwrite(root->fs_info->sb);
+       if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
+               if (type == TRANS_JOIN_FREEZE)
+                       return ERR_PTR(-EPERM);
+               sb_start_intwrite(root->fs_info->sb);
+       }
 
        if (may_wait_transaction(root, type))
                wait_current_trans(root);
@@ -424,6 +429,11 @@ struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root
        return start_transaction(root, 0, TRANS_USERSPACE, 0);
 }
 
+struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root)
+{
+       return start_transaction(root, 0, TRANS_JOIN_FREEZE, 0);
+}
+
 /* wait for a transaction commit to be fully complete */
 static noinline void wait_for_commit(struct btrfs_root *root,
                                    struct btrfs_transaction *commit)

diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index b6463e128048e461858a4c9163061bb323ce766e..fbf8313b9d67463d5da5a3d6cc273f655287aa65 100644 (file)
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -102,6 +102,7 @@ struct btrfs_trans_handle *btrfs_start_transaction_noflush(
                                        struct btrfs_root *root, int num_items);
 struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root);
 struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root);
+struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root);
 struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root);
 int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid);
 int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,