| Message ID | 20200320183436.16908-5-josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Relocation and backref resolution fixes | expand |
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index 9d0f87df2c35..0dcc11644be4 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -523,6 +523,12 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info, goto out_free; } + if (!path->search_commit_root && + test_bit(BTRFS_ROOT_DELETING, &root->state)) { + ret = -ENOENT; + goto out; + } + if (btrfs_is_testing(fs_info)) { ret = -ENOENT; goto out;
Zygo reported a deadlock where a task was stuck in the inode logical resolve code. The deadlock looks like this Task 1 btrfs_ioctl_logical_to_ino ->iterate_inodes_from_logical ->iterate_extent_inodes ->path->search_commit_root isn't set, so a transaction is started ->resolve_indirect_ref for a root that's being deleted ->search for our key, attempt to lock a node, DEADLOCK Task 2 btrfs_drop_snapshot ->walk down to a leaf, lock it, walk up, lock node ->end transaction ->start transaction -> wait_cur_trans Task 3 btrfs_commit_transaction ->wait_event(cur_trans->write_wait, num_writers == 1) DEADLOCK We are holding a transaction open in btrfs_ioctl_logical_to_ino while we try to resolve our references. btrfs_drop_snapshot() holds onto its locks while it stops and starts transaction handles, because it assumes nobody is going to touch the root now. Commit just does what commit does, waiting for the writers to finish, blocking any new trans handles from starting. Fix this by making the backref code not try to resolve backrefs of roots that are currently being deleted. This will keep us from walking into a snapshot that's currently being deleted. This problem was harder to hit before because we rarely broke out of the snapshot delete halfway through, but with my delayed ref throttling code it happened much more often. However we've always been able to do this, so it's not a new problem. Fixes: 8da6d5815c59 ("Btrfs: added btrfs_find_all_roots()") Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/backref.c | 6 ++++++ 1 file changed, 6 insertions(+)