From: Tejun Heo <tj@kernel.org>
To: Mandeep Singh Baines <msb@chromium.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
linux-kernel@vger.kernel.org,
containers@lists.linux-foundation.org, cgroups@vger.kernel.org,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Oleg Nesterov <oleg@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Paul Menage <paul@paulmenage.org>
Subject: Re: [PATCH 1/2] cgroup: remove tasklist_lock from cgroup_attach_proc
Date: Thu, 22 Dec 2011 14:51:02 -0800 [thread overview]
Message-ID: <20111222225102.GM17084@google.com> (raw)
In-Reply-To: <1324592816-13792-1-git-send-email-msb@chromium.org>
Hello,
On Thu, Dec 22, 2011 at 02:26:55PM -0800, Mandeep Singh Baines wrote:
> @@ -2283,14 +2261,26 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
>
> threadgroup_lock(tsk);
>
> - if (threadgroup)
> + if (threadgroup) {
> + if (!thread_group_leader(tsk)) {
> + /*
> + * a race with de_thread from another thread's exec()
> + * may strip us of our leadership, if this happens,
> + * there is no choice but to throw this task away and
> + * try again (from cgroup_procs_write); this is
> + * "double-double-toil-and-trouble-check locking".
> + */
> + ret = -EAGAIN;
> + goto out_unlock_threadgroup;
> + }
> ret = cgroup_attach_proc(cgrp, tsk);
Ummm... can't we just do tsk = tsk->leader after locking threadgroup?
Why do we need to retry from the beginning?
Thanks.
--
tejun
next prev parent reply other threads:[~2011-12-22 22:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-22 22:26 [PATCH 1/2] cgroup: remove tasklist_lock from cgroup_attach_proc Mandeep Singh Baines
2011-12-22 22:26 ` [PATCH 2/2] cgroup: remove extra calls to find_existing_css_set Mandeep Singh Baines
2011-12-22 23:12 ` Tejun Heo
2011-12-23 0:29 ` Mandeep Singh Baines
2011-12-22 22:51 ` Tejun Heo [this message]
2011-12-23 0:58 ` [PATCH 1/2] cgroup: remove tasklist_lock from cgroup_attach_proc Mandeep Singh Baines
-- strict thread matches above, loose matches on Subject: below --
2011-12-23 2:52 Mandeep Singh Baines
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