From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 2/5] cgroup: remove redundant get/put of task struct Date: Tue, 20 Dec 2011 15:23:26 -0800 Message-ID: <20111220232326.GL10752@google.com> References: <1324422873-31001-1-git-send-email-msb@chromium.org> <1324422873-31001-3-git-send-email-msb@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=MGU8SjF+5c1cmm2EqWiDHOUj79rzuwWZKSWQR/WIBeg=; b=e2ZZq5w+SXYuVMzxv12t18nf8GlxUne5qtDlV5PJJVKRghQE3iqMzHHHj+/kgs9XYX uM7eXJrt1ad/fdM7fYwv/G9ilt97VAA0zMMT316oVG3bAVj6bdtiFElspS/gDDYpwdMO rivwXkCbL2ptg8iHxvLuxY7c/i0wMnLxAJ7T8= Content-Disposition: inline In-Reply-To: <1324422873-31001-3-git-send-email-msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Mandeep Singh Baines Cc: Frederic Weisbecker , containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, LKML , Oleg Nesterov , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , Paul Menage Hello, On Tue, Dec 20, 2011 at 03:14:30PM -0800, Mandeep Singh Baines wrote: > @@ -2287,14 +2280,12 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup) > cgroup_unlock(); > return -EACCES; > } > - get_task_struct(tsk); > rcu_read_unlock(); This is before threadgroup is locked. What guarantees @tsk doesn't go away once rcu is unlocked? Thanks. -- tejun