Messages in this thread Patch in this message | | | 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 |
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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 <fweisbec@gmail.com> Signed-off-by: Mandeep Singh Baines <msb@chromium.org> Cc: Tejun Heo <tj@kernel.org> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: containers@lists.linux-foundation.org Cc: cgroups@vger.kernel.org Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Paul Menage <paul@paulmenage.org> --- 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
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