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    SubjectRe: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts
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    > > @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
    > > int flag)
    > > {
    > > struct super_block *sb = old->mnt_sb;
    > > - struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
    > > + struct vfsmount *mnt;
    > >
    > > + if (flag & CL_SETUSER) {
    > > + int err = reserve_user_mount();
    > > + if (err)
    > > + return ERR_PTR(err);
    > > + }
    > > + mnt = alloc_vfsmnt(old->mnt_devname);
    > > if (!mnt)
    > > - return ERR_PTR(-ENOMEM);
    > > + goto alloc_failed;
    > >
    > > mnt->mnt_flags = old->mnt_flags;
    > > atomic_inc(&sb->s_active);
    >
    > I think there's a little race here. We could have several users racing
    > to get to this point when nr_user_mounts==max_user_mounts-1. One user
    > wins the race and gets their mount reserved. The others get the error
    > out of reserve_user_mount(), and return.
    >
    > But, the winner goes on to error out on some condition further down in
    > clone_mnt() and never actually instantiates the mount.
    >
    > Do you think this is a problem?

    For similar reasons as stated in the previous mail, I don't think this
    matters. If nr_user_mounts is getting remotely close to
    max_user_mounts, then something is wrong (or the max needs to be
    raised anyway).

    Thanks for the review, Dave!

    Miklos


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