On 2018/11/20 上午12:20, fdman...@kernel.org wrote: > From: Filipe Manana <fdman...@suse.com> > > 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. > > Signed-off-by: Filipe Manana <fdman...@suse.com>
Reviewed-by: Qu Wenruo <w...@suse.com>
Thanks,
Qu
> ---
> fs/btrfs/qgroup.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index ae1358253b7b..0bdf28499790 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -2250,7 +2250,7 @@ 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;
> @@ -2260,6 +2260,7 @@ 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;
>
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