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authorJosef Bacik <jbacik@fb.com>2014-03-06 19:01:07 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-04-26 17:19:05 -0700
commit50b51ee3114bfce0ab7cadead016f2801588f1ca (patch)
tree3db56bcf6f11280c029635373549f8925b295e86
parent53dcb28868912eea366550ce30c0f5e17cbf0099 (diff)
Btrfs: fix deadlock with nested trans handles
commit 3bbb24b20a8800158c33eca8564f432dd14d0bf3 upstream. Zach found this deadlock that would happen like this btrfs_end_transaction <- reduce trans->use_count to 0 btrfs_run_delayed_refs btrfs_cow_block find_free_extent btrfs_start_transaction <- increase trans->use_count to 1 allocate chunk btrfs_end_transaction <- decrease trans->use_count to 0 btrfs_run_delayed_refs lock tree block we are cowing above ^^ We need to only decrease trans->use_count if it is above 1, otherwise leave it alone. This will make nested trans be the only ones who decrease their added ref, and will let us get rid of the trans->use_count++ hack if we have to commit the transaction. Thanks, Reported-by: Zach Brown <zab@redhat.com> Signed-off-by: Josef Bacik <jbacik@fb.com> Tested-by: Zach Brown <zab@redhat.com> Signed-off-by: Chris Mason <clm@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/btrfs/transaction.c14
1 files changed, 4 insertions, 10 deletions
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 34cd83184c4a..b05bf58b9395 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -683,7 +683,8 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
int lock = (trans->type != TRANS_JOIN_NOLOCK);
int err = 0;
- if (--trans->use_count) {
+ if (trans->use_count > 1) {
+ trans->use_count--;
trans->block_rsv = trans->orig_rsv;
return 0;
}
@@ -731,17 +732,10 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
}
if (lock && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
- if (throttle) {
- /*
- * We may race with somebody else here so end up having
- * to call end_transaction on ourselves again, so inc
- * our use_count.
- */
- trans->use_count++;
+ if (throttle)
return btrfs_commit_transaction(trans, root);
- } else {
+ else
wake_up_process(info->transaction_kthread);
- }
}
if (trans->type & __TRANS_FREEZABLE)