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| author | Frederic Weisbecker <fweisbec@gmail.com> | 2011-12-21 20:03:18 +0100 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2011-12-21 11:15:01 -0800 |
| commit | c84cdf75ccb2845f690579e838f13f7e744e3d23 (patch) | |
| tree | a94bd69e84e7996852e1973c75fe11a2b0f1a42d /kernel/cgroup.c | |
| parent | 7e381b0eb1e1a9805c37335562e8dc02e7d7848c (diff) | |
| download | blackbird-op-linux-c84cdf75ccb2845f690579e838f13f7e744e3d23.tar.gz blackbird-op-linux-c84cdf75ccb2845f690579e838f13f7e744e3d23.zip | |
cgroup: Remove unnecessary task_lock before fetching css_set on migration
When we fetch the css_set of the tasks on cgroup migration, we don't need
anymore to synchronize against cgroup_exit() that could swap the old one
with init_css_set. Now that we are using threadgroup_lock() during
the migrations, we don't need to worry about it anymore.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Containers <containers@lists.linux-foundation.org>
Cc: Cgroups <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>
Diffstat (limited to 'kernel/cgroup.c')
| -rw-r--r-- | kernel/cgroup.c | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index dae50d0d8e4b..4936d8886b4f 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1850,14 +1850,14 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, struct css_set *newcg; /* - * get old css_set. we need to take task_lock and refcount it, because - * an exiting task can change its css_set to init_css_set and drop its - * old one without taking cgroup_mutex. + * get old css_set. We are synchronized through threadgroup_lock() + * against PF_EXITING setting such that we can't race against + * cgroup_exit() changing the css_set to init_css_set and dropping the + * old one. */ - task_lock(tsk); + WARN_ON_ONCE(tsk->flags & PF_EXITING); oldcg = tsk->cgroups; get_css_set(oldcg); - task_unlock(tsk); /* locate or allocate a new css_set for this task. */ if (guarantee) { @@ -1879,9 +1879,7 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, } put_css_set(oldcg); - /* @tsk can't exit as its threadgroup is locked */ task_lock(tsk); - WARN_ON_ONCE(tsk->flags & PF_EXITING); rcu_assign_pointer(tsk->cgroups, newcg); task_unlock(tsk); @@ -2182,11 +2180,13 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) /* nothing to do if this task is already in the cgroup */ if (tc->cgrp == cgrp) continue; - /* get old css_set pointer */ - task_lock(tc->task); + /* + * get old css_set pointer. threadgroup is locked so this is + * safe against concurrent cgroup_exit() changing this to + * init_css_set. + */ oldcg = tc->task->cgroups; get_css_set(oldcg); - task_unlock(tc->task); /* see if the new one for us is already in the list? */ if (css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) { /* was already there, nothing to do. */ |
