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-rw-r--r--fs/btrfs/ioctl.c33
1 files changed, 30 insertions, 3 deletions
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 6b93fae744..8851ba7a1e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3722,15 +3722,43 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
goto drop_write;
}
- down_write(&fs_info->subvol_sem);
-
switch (sa->cmd) {
case BTRFS_QUOTA_CTL_ENABLE:
case BTRFS_QUOTA_CTL_ENABLE_SIMPLE_QUOTA:
+ down_write(&fs_info->subvol_sem);
ret = btrfs_quota_enable(fs_info, sa);
+ up_write(&fs_info->subvol_sem);
break;
case BTRFS_QUOTA_CTL_DISABLE:
+ /*
+ * Lock the cleaner mutex to prevent races with concurrent
+ * relocation, because relocation may be building backrefs for
+ * blocks of the quota root while we are deleting the root. This
+ * is like dropping fs roots of deleted snapshots/subvolumes, we
+ * need the same protection.
+ *
+ * This also prevents races between concurrent tasks trying to
+ * disable quotas, because we will unlock and relock
+ * qgroup_ioctl_lock across BTRFS_FS_QUOTA_ENABLED changes.
+ *
+ * We take this here because we have the dependency of
+ *
+ * inode_lock -> subvol_sem
+ *
+ * because of rename. With relocation we can prealloc extents,
+ * so that makes the dependency chain
+ *
+ * cleaner_mutex -> inode_lock -> subvol_sem
+ *
+ * so we must take the cleaner_mutex here before we take the
+ * subvol_sem. The deadlock can't actually happen, but this
+ * quiets lockdep.
+ */
+ mutex_lock(&fs_info->cleaner_mutex);
+ down_write(&fs_info->subvol_sem);
ret = btrfs_quota_disable(fs_info);
+ up_write(&fs_info->subvol_sem);
+ mutex_unlock(&fs_info->cleaner_mutex);
break;
default:
ret = -EINVAL;
@@ -3738,7 +3766,6 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
}
kfree(sa);
- up_write(&fs_info->subvol_sem);
drop_write:
mnt_drop_write_file(file);
return ret;