linux-kernel - Re: [PATCH v1 2/4] pid: add pidctl()

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Message-ID: <20190326171525.GA116974@google.com>
Date:   Tue, 26 Mar 2019 13:15:25 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Christian Brauner <christian@...uner.io>
Cc:     jannh@...gle.com, khlebnikov@...dex-team.ru, luto@...nel.org,
        dhowells@...hat.com, serge@...lyn.com, ebiederm@...ssion.com,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnd@...db.de, keescook@...omium.org, adobriyan@...il.com,
        tglx@...utronix.de, mtk.manpages@...il.com, bl0pbl33p@...il.com,
        ldv@...linux.org, akpm@...ux-foundation.org, oleg@...hat.com,
        nagarathnam.muthusamy@...cle.com, cyphar@...har.com,
        viro@...iv.linux.org.uk, dancol@...gle.com
Subject: Re: [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