Btrfs: fix race during transaction joins
While we're allocating ram for a new transaction, we drop our spinlock.
When we get the lock back, we do check to see if a transaction started
while we slept, but we don't check to make sure it isn't blocked
because a commit has already started.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 29f782cc..960835e 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -55,6 +55,7 @@
struct btrfs_transaction *cur_trans;
spin_lock(&root->fs_info->trans_lock);
+loop:
if (root->fs_info->trans_no_join) {
if (!nofail) {
spin_unlock(&root->fs_info->trans_lock);
@@ -75,16 +76,18 @@
cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
if (!cur_trans)
return -ENOMEM;
+
spin_lock(&root->fs_info->trans_lock);
if (root->fs_info->running_transaction) {
+ /*
+ * someone started a transaction after we unlocked. Make sure
+ * to redo the trans_no_join checks above
+ */
kmem_cache_free(btrfs_transaction_cachep, cur_trans);
cur_trans = root->fs_info->running_transaction;
- atomic_inc(&cur_trans->use_count);
- atomic_inc(&cur_trans->num_writers);
- cur_trans->num_joined++;
- spin_unlock(&root->fs_info->trans_lock);
- return 0;
+ goto loop;
}
+
atomic_set(&cur_trans->num_writers, 1);
cur_trans->num_joined = 0;
init_waitqueue_head(&cur_trans->writer_wait);