From: David Howells <dhowells@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: dhowells@redhat.com, Christoph Hellwig <hch@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
James Morris <jmorris@namei.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Roland McGrath <roland@redhat.com>,
Stephen Smalley <sds@tycho.nsa.gov>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 -mm 2/2] current_is_single_threaded: don't use ->mmap_sem
Date: Fri, 10 Jul 2009 15:07:42 +0100 [thread overview]
Message-ID: <25973.1247234862@redhat.com> (raw)
In-Reply-To: <20090710014857.GC4723@redhat.com>
Oleg Nesterov <oleg@redhat.com> wrote:
> current_is_single_threaded() can safely miss a freshly forked CLONE_VM
> task, but in this case it must not miss its parent. That is why we take
> mm->mmap_sem for writing to make sure a thread/task with the same ->mm
> can't pass exit_mm() and disappear.
>
> However we can avoid ->mmap_sem and rely on rcu/barriers:
>
> - if we do not see the exiting parent on thread/process list
> we see the result of list_del_rcu(), in this case we must
> also see the result of list_add_rcu() which does wmb().
>
> - if we do see the parent but its ->mm == NULL, we need rmb()
> to make sure we can't miss the child.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
next prev parent reply other threads:[~2009-07-10 14:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-09 21:28 [PATCH -mm 1/2] rename is_single_threaded(task) to is_current_single_threaded(void) Oleg Nesterov
2009-07-09 23:04 ` James Morris
2009-07-10 1:33 ` Christoph Hellwig
2009-07-10 1:46 ` Oleg Nesterov
2009-07-10 1:48 ` [PATCH v2 -mm 1/2] rename is_single_threaded(task) to current_is_single_threaded(void) Oleg Nesterov
2009-07-10 14:07 ` David Howells
2009-07-10 1:48 ` [PATCH v2 -mm 2/2] current_is_single_threaded: don't use ->mmap_sem Oleg Nesterov
2009-07-10 14:07 ` David Howells [this message]
2009-07-12 22:12 ` James Morris
2009-07-13 23:56 ` Oleg Nesterov
2009-07-16 23:41 ` James Morris
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