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    SubjectRe: [PATCH v1 2/4] pid: add pidctl()
    On Tue, Mar 26, 2019 at 06:08:28PM +0100, Christian Brauner wrote:
    [snip]
    > > > + struct pid *struct_pid;
    > > > + pid_t result;
    > > > +
    > > > + if (flags)
    > > > + return -EINVAL;
    > > > +
    > > > + switch (cmd) {
    > > > + case PIDCMD_QUERY_PID:
    > > > + break;
    > > > + case PIDCMD_QUERY_PIDNS:
    > > > + if (pid)
    > > > + return -EINVAL;
    > > > + break;
    > > > + case PIDCMD_GET_PIDFD:
    > > > + break;
    > > > + default:
    > > > + return -EOPNOTSUPP;
    > > > + }
    > > > +
    > > > + source_ns = get_pid_ns_by_fd(source);
    > > > + if (IS_ERR(source_ns))
    > > > + return PTR_ERR(source_ns);
    > > > +
    > > > + target_ns = get_pid_ns_by_fd(target);
    > > > + if (IS_ERR(target_ns)) {
    > > > + put_pid_ns(source_ns);
    > > > + return PTR_ERR(target_ns);
    > > > + }
    > > > +
    > > > + if (cmd == PIDCMD_QUERY_PIDNS) {
    > > > + result = pidns_related(source_ns, target_ns);
    > > > + } else {
    > > > + rcu_read_lock();
    > > > + struct_pid = get_pid(find_pid_ns(pid, source_ns));
    > > > + rcu_read_unlock();
    > > > +
    > > > + if (struct_pid)
    > > > + result = pid_nr_ns(struct_pid, target_ns);
    > > > + else
    > > > + result = -ESRCH;
    > > > +
    > > > + if (cmd == PIDCMD_GET_PIDFD && (result > 0))
    > > > + result = pidfd_create_fd(struct_pid, O_CLOEXEC);
    > >
    > > pidfd_create_fd already does put_pid on errors..
    >
    > it also takes its own reference
    >
    > >
    > > > +
    > > > + if (!result)
    > > > + result = -ENOENT;
    > > > +
    > > > + put_pid(struct_pid);
    > >
    > > so on error you would put_pid twice which seems odd.. I would suggest, don't
    > > release the pid ref from within pidfd_create_fd, release the ref from the
    > > caller. Speaking of which, I added to my list to convert the pid->count to
    > > refcount_t at some point :)
    >
    > as i said, pidfd_create_fd takes its own reference

    Oh. That was easy to miss. Fair enough. I take that comment back.

    Please also reply to the other comments I posted, thanks. Generally on LKML,
    I have seen there is an expectation to reply to all reviewer's review
    comments even if you agree with them. This helps keep the review going
    smoothly. Just my 2 cents.

    thanks,

    - Joel

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