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From: Christian Brauner <christian.brauner@ubuntu.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-kernel@vger.kernel.org, Shuah Khan <shuah@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>,
	Christian Kellner <christian@kellner.me>,
	Roman Gushchin <guro@fb.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Aleksa Sarai <cyphar@cyphar.com>,
	"Dmitry V. Levin" <ldv@altlinux.org>,
	linux-kselftest@vger.kernel.org, Jann Horn <jannh@google.com>,
	linux-api@vger.kernel.org
Subject: Re: [PATCH 1/2] pidfd: verify task is alive when printing fdinfo
Date: Tue, 15 Oct 2019 16:56:47 +0200	[thread overview]
Message-ID: <20191015145646.72eqrw6j52ehvfn2@wittgenstein> (raw)
In-Reply-To: <20191015144356.GA16978@redhat.com>

On Tue, Oct 15, 2019 at 04:43:57PM +0200, Oleg Nesterov wrote:
> On 10/15, Christian Brauner wrote:
> >
> > +static inline bool task_alive(struct pid *pid)
> > +{
> > +	bool alive = true;
> > +
> > +	rcu_read_lock();
> > +	if (!pid_task(pid, PIDTYPE_PID))
> > +		alive = false;
> > +	rcu_read_unlock();
> > +
> > +	return alive;
> > +}
> 
> Well, the usage of rcu_read_lock/unlock looks confusing to me...
> 
> I mean, this helper does not need rcu lock at all. Except
> rcu_dereference_check() will complain.

Yep, I think we have another codepath were the rcu locks might be purely
cosmetic so I thought it's not a big deal (see below).

> 
> 	static inline bool task_alive(struct pid *pid)
> 	{
> 		bool alive;
> 
> 		/* shut up rcu_dereference_check() */
> 		rcu_lock_acquire(&rcu_lock_map);
> 		alive = !!pid_task(pid, PIDTYPE_PID));
> 		rcu_lock_release(&rcu_lock_map);
> 
> 		return alive;
> 	}
> 
> looks more clear imo.
> 
> But in fact I'd suggest to simply use !hlist_empty(&pid->tasks[PIDTYPE_PID])
> in pidfd_show_fdinfo() and do not add a new helper.

Sounds good to me. But can't we then just do something similar just with
!hlist_empty(&pid->tasks[PIDTYPE_TGID])

in v5.4-rc3:kernel/pid.c:pidfd_open():514-517 ?

or would this be problematic because of de_thread()?

Thanks!
Christian

  reply	other threads:[~2019-10-15 14:56 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-15 14:13 Christian Brauner
2019-10-15 14:13 ` [PATCH 2/2] test: verify fdinfo for pidfd of reaped process Christian Brauner
2019-10-16 12:07   ` Christian Kellner
2019-10-15 14:43 ` [PATCH 1/2] pidfd: verify task is alive when printing fdinfo Oleg Nesterov
2019-10-15 14:56   ` Christian Brauner [this message]
2019-10-15 15:43     ` Oleg Nesterov
2019-10-16 15:36 ` [PATCH v2 1/5] " Christian Brauner
2019-10-16 15:36   ` [PATCH v2 2/5] test: verify fdinfo for pidfd of reaped process Christian Brauner
2019-10-16 15:36   ` [PATCH v2 3/5] pid: use task_alive() in __change_pid() Christian Brauner
2019-10-16 15:36   ` [PATCH v2 4/5] exit: use task_alive() in do_wait() Christian Brauner
2019-10-16 15:36   ` [PATCH v2 5/5] pid: use task_alive() in pidfd_open() Christian Brauner
2019-10-16 16:24   ` [PATCH v2 1/5] pidfd: verify task is alive when printing fdinfo Oleg Nesterov
2019-10-16 16:31     ` Christian Brauner
2019-10-17  8:54       ` Oleg Nesterov
2019-10-17 10:18   ` [PATCH v3 1/5] pidfd: check pid has attached task in fdinfo Christian Brauner
2019-10-17 10:18     ` [PATCH v3 2/5] test: verify fdinfo for pidfd of reaped process Christian Brauner
2019-10-17 10:18     ` [PATCH v3 3/5] pid: use pid_has_task() in __change_pid() Christian Brauner
2019-10-17 10:18     ` [PATCH v3 4/5] exit: use pid_has_task() in do_wait() Christian Brauner
2019-10-17 10:18     ` [PATCH v3 5/5] pid: use pid_has_task() in pidfd_open() Christian Brauner
2019-10-18 15:05     ` [PATCH v3 1/5] pidfd: check pid has attached task in fdinfo Christian Brauner

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