From: Al Viro <viro@ZenIV.linux.org.uk>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Pavel Emelyanov <xemul@openvz.org>,
Serge Hallyn <serge.hallyn@canonical.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
"Dmitry V. Levin" <ldv@altlinux.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Doug Ledford <dledford@redhat.com>,
linux-kernel@vger.kernel.org,
containers@lists.linux-foundation.org
Subject: Re: [PATCH v2] ns: do not block exit_task_namespaces() for a long time
Date: Mon, 16 Jul 2012 17:53:01 +0100 [thread overview]
Message-ID: <20120716165301.GN31729@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1342451364-14787-1-git-send-email-kirill.shutemov@linux.intel.com>
On Mon, Jul 16, 2012 at 06:09:24PM +0300, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> On exiting of the last task in a namespace we need to trigger freeing of
> the namespace. Currently, we call synchronize_rcu() and free_nsproxy()
> directly on do_exit() path.
>
> On my machine synchronize_rcu() blocks for about 0.01 seconds. For
> comparing: normal exit_group() syscall takes less than 0.0003 seconds.
>
> Let's offload synchronize_rcu() and free_nsproxy() to a workqueue.
>
> I also move synchronize_rcu() inside free_nsproxy(). It fixes racy
> put_nsproxy() which calls free_nsproxy() without synchronize_rcu().
> I guess it was missed during switch to RCU (see cf7b708).
NAK. Making final umounts of anything in that namespace asynchronous,
even though nothing is holding the stuff on them busy is simply
wrong. Note that they can take a _long_ time, so we are talking about
minutes worth of delay in the worst case. It's user-visible and
it's a serious potential for trouble.
next prev parent reply other threads:[~2012-07-16 16:53 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-13 11:48 [PATCH] ns: move free_nsproxy() out of do_exit() path Kirill A. Shutemov
2012-07-13 21:08 ` Andrew Morton
2012-07-13 22:23 ` Kirill A. Shutemov
2012-07-16 15:09 ` [PATCH v2] ns: do not block exit_task_namespaces() for a long time Kirill A. Shutemov
2012-07-16 15:39 ` Myklebust, Trond
2012-07-16 16:39 ` Kirill A. Shutemov
2012-07-16 16:53 ` Myklebust, Trond
2012-07-16 16:53 ` Al Viro [this message]
2012-07-16 17:16 ` Kirill A. Shutemov
2012-07-16 17:22 ` Al Viro
2012-07-16 21:05 ` Kirill A. Shutemov
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