From: Pavel Emelyanov <xemul@openvz.org>
To: David Howells <dhowells@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>,
jmorris@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: Request for documentation of PID handling functions
Date: Wed, 30 Jul 2008 06:04:04 +0400 [thread overview]
Message-ID: <488FCC14.3070208@openvz.org> (raw)
In-Reply-To: <21590.1217285986@redhat.com>
David Howells wrote:
> Hi Pavel,
>
> Can you please provide documentation for the PID handling functions you
> supplied in commit:
>
> 7af5729474b5b8ad385adadab78d6e723e7655a3
>
> In particular I'd like to know what locks are required when. I'm trying to
> determine if in this piece of code:
>
> read_lock(&tasklist_lock);
> ret = 0;
> if (pid != task_pid_vnr(current))
> ret = -EPERM;
> read_unlock(&tasklist_lock);
>
> the lock of tasklist_lock is necessary.
The RCU protection is enough to get pids from tasks. However, the pids
are detached under the tasklist lock write-locked, so provided you're
*already* sitting under it the RCU is excessive.
However, Oleg pointed me out some time ago, that in some cases RCU-only
protection was not enough in some cases, so I put him in Cc.
> David
>
next prev parent reply other threads:[~2008-07-30 2:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-28 22:59 Request for documentation of PID handling functions David Howells
2008-07-30 2:04 ` Pavel Emelyanov [this message]
2008-07-30 9:56 ` Oleg Nesterov
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