From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mandeep Singh Baines Subject: [PATCH 2/3] cgroup: replace tasklist_lock with rcu_read_lock Date: Tue, 3 Jan 2012 21:18:31 -0800 Message-ID: <1325654312-32477-2-git-send-email-msb@chromium.org> References: <1325654312-32477-1-git-send-email-msb@chromium.org> Return-path: In-Reply-To: <1325654312-32477-1-git-send-email-msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo , Li Zefan , Frederic Weisbecker , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: Mandeep Singh Baines , Tejun Heo , Li Zefan , containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, KAMEZAWA Hiroyuki , Oleg Nesterov , Andrew Morton , Paul Menage We can replace the tasklist_lock in cgroup_attach_proc with an rcu_read_lock. Changes in V4: * https://lkml.org/lkml/2011/12/23/284 (Frederic Weisbecker) * Minimize size of rcu_read_lock critical section * Add comment * https://lkml.org/lkml/2011/12/26/136 (Li Zefan) * Split into two patches Changes in V3: * https://lkml.org/lkml/2011/12/22/419 (Frederic Weisbecker) * Add an rcu_read_lock to protect against exit Changes in V2: * https://lkml.org/lkml/2011/12/22/86 (Tejun Heo) * Use a goto instead of returning -EAGAIN Suggested-by: Frederic Weisbecker Signed-off-by: Mandeep Singh Baines Cc: Tejun Heo Cc: Li Zefan Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage --- kernel/cgroup.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 09867eb..354c539 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2102,10 +2102,14 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) if (retval) goto out_free_group_list; - /* prevent changes to the threadgroup list while we take a snapshot. */ - read_lock(&tasklist_lock); tsk = leader; i = 0; + /* + * Prevent freeing of tasks while we take a snapshot. Tasks that are + * already PF_EXITING could be freed from underneath us unless we + * take an rcu_read_lock. + */ + rcu_read_lock(); do { struct task_and_cgroup ent; @@ -2128,11 +2132,11 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) BUG_ON(retval != 0); i++; } while_each_thread(leader, tsk); + rcu_read_unlock(); /* remember the number of threads in the array for later. */ group_size = i; tset.tc_array = group; tset.tc_array_len = group_size; - read_unlock(&tasklist_lock); /* methods shouldn't be called if no task is actually migrating */ retval = 0; -- 1.7.3.1