From: Oleg Nesterov <oleg@redhat.com>
To: Jiri Slaby <jslaby@suse.cz>
Cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com,
tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com, jmorris@namei.org
Subject: Re: [PATCH RFC] pid: make setpgid() system call use RCU read-side critical section
Date: Fri, 10 Sep 2010 00:15:55 +0200 [thread overview]
Message-ID: <20100909221555.GB6273@redhat.com> (raw)
In-Reply-To: <4C7C0BAB.3000709@suse.cz>
On 08/30, Jiri Slaby wrote:
>
> Ccing Oleg.
Sorry for delay...
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -938,6 +938,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid)
> > write_lock_irq(&tasklist_lock);
> >
> > err = -ESRCH;
> > + rcu_read_lock();
> > p = find_task_by_vpid(pid);
>
> AFAICT the missing lock doesn't harm due to the write_lock of tasklist
> above. But is probably a good thing to do anyway.
The problem is, find_task_by_vpid() is not safe without RCU. It is not
that the returned task_struct can't go away, find_pid_ns() itself is
not safe. This is because the failing copy_process() calls free_pid()
without tasklist_lock and modifies pid_hash[] list.
Oleg.
next prev parent reply other threads:[~2010-09-09 22:20 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-30 17:26 [PATCH RFC] pid: make setpgid() system call use RCU read-side critical section Paul E. McKenney
2010-08-30 19:51 ` Jiri Slaby
2010-08-30 20:32 ` Paul E. McKenney
2010-09-09 22:15 ` Oleg Nesterov [this message]
2010-09-16 9:18 ` Jiri Slaby
2010-09-16 16:39 ` Oleg Nesterov
2010-08-31 13:02 ` David Howells
2010-08-31 15:12 ` Paul E. McKenney
2010-08-31 15:31 ` David Howells
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