The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 552f0329c75b3e1d7f9bb8c9e421d37403f192cd Mon Sep 17 00:00:00 2001

From: Filipe Manana fdmanana@suse.com Date: Mon, 19 Nov 2018 16:20:34 +0000 Subject: [PATCH] Btrfs: fix race between enabling quotas and subvolume creation

We have a race between enabling quotas end subvolume creation that cause subvolume creation to fail with -EINVAL, and the following diagram shows how it happens:

CPU 0 CPU 1

btrfs_ioctl() btrfs_ioctl_quota_ctl() btrfs_quota_enable() mutex_lock(fs_info->qgroup_ioctl_lock)

btrfs_ioctl() create_subvol() btrfs_qgroup_inherit() -> save fs_info->quota_root into quota_root -> stores a NULL value -> tries to lock the mutex qgroup_ioctl_lock -> blocks waiting for the task at CPU0

-> sets BTRFS_FS_QUOTA_ENABLED in fs_info -> sets quota_root in fs_info->quota_root (non-NULL value)

mutex_unlock(fs_info->qgroup_ioctl_lock)

-> checks quota enabled flag is set -> returns -EINVAL because fs_info->quota_root was NULL before it acquired the mutex qgroup_ioctl_lock -> ioctl returns -EINVAL

Returning -EINVAL to user space will be confusing if all the arguments passed to the subvolume creation ioctl were valid.

Fix it by grabbing the value from fs_info->quota_root after acquiring the mutex.

CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 45868fd76209..f70825af6438 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -2659,7 +2659,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, int i; u64 *i_qgroups; struct btrfs_fs_info *fs_info = trans->fs_info; - struct btrfs_root *quota_root = fs_info->quota_root; + struct btrfs_root *quota_root; struct btrfs_qgroup *srcgroup; struct btrfs_qgroup *dstgroup; u32 level_size = 0; @@ -2669,6 +2669,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) goto out;

+ quota_root = fs_info->quota_root; if (!quota_root) { ret = -EINVAL; goto out;