btrfs: Take trans lock before access running trans in check_delayed_ref

In preivous patch:
Btrfs: kill trans in run_delalloc_nocow and btrfs_cross_ref_exist
We avoid starting btrfs transaction and get this information from
fs_info->running_transaction directly.

When accessing running_transaction in check_delayed_ref, there's a
chance that current transaction will be freed by commit transaction
after the NULL pointer check of running_transaction is passed.

After looking all the other places using fs_info->running_transaction,
they are either protected by trans_lock or holding the transactions.

Fix this by using trans_lock and increasing the use_count.

Fixes: e4c3b2dcd144 ("Btrfs: kill trans in run_delalloc_nocow and btrfs_cross_ref_exist")
CC: stable@vger.kernel.org # 4.14+
Signed-off-by: ethanwu <ethanwu@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index f99102063366dbd335ab1540bf2034f8ec07af96..3871658b6ab1de7b5a87200fb252a87f54fdef9a 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3142,7 +3142,11 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
        struct rb_node *node;
        int ret = 0;
 
+       spin_lock(&root->fs_info->trans_lock);
        cur_trans = root->fs_info->running_transaction;
+       if (cur_trans)
+               refcount_inc(&cur_trans->use_count);
+       spin_unlock(&root->fs_info->trans_lock);
        if (!cur_trans)
                return 0;
 
@@ -3151,6 +3155,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
        head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
        if (!head) {
                spin_unlock(&delayed_refs->lock);
+               btrfs_put_transaction(cur_trans);
                return 0;
        }
 
@@ -3167,6 +3172,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
                mutex_lock(&head->mutex);
                mutex_unlock(&head->mutex);
                btrfs_put_delayed_ref_head(head);
+               btrfs_put_transaction(cur_trans);
                return -EAGAIN;
        }
        spin_unlock(&delayed_refs->lock);
@@ -3199,6 +3205,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
        }
        spin_unlock(&head->lock);
        mutex_unlock(&head->mutex);
+       btrfs_put_transaction(cur_trans);
        return ret;
 }