[PATCH 2/2 v2] cgroup: Drop task_lock(parent) on cgroup_fork()
From: Frederic Weisbecker <hidden>
Date: 2011-12-21 02:03:07
Also in:
lkml
Subsystem:
the rest · Maintainer:
Linus Torvalds
We don't need to hold the parent task_lock() on the parent in cgroup_fork() because we are already synchronized against the two places that may change the parent css_set concurrently: - cgroup_exit(), but the parent obviously can't exit concurrently - cgroup migration: we are synchronized against threadgroup_lock() So we can safely remove the task_lock() there. Signed-off-by: Frederic Weisbecker <redacted> Cc: Tejun Heo <redacted> Cc: Li Zefan <redacted> Cc: Containers <redacted> Cc: Cgroups <redacted> Cc: KAMEZAWA Hiroyuki <redacted> Cc: Oleg Nesterov <redacted> Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> Cc: Paul Menage <redacted> Cc: Mandeep Singh Baines <redacted> --- kernel/cgroup.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 24f6d6f..1999f60 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c@@ -4556,7 +4556,7 @@ static const struct file_operations proc_cgroupstats_operations = { * * A pointer to the shared css_set was automatically copied in * fork.c by dup_task_struct(). However, we ignore that copy, since - * it was not made under the protection of RCU or cgroup_mutex, so + * it was not made under the protection of threadgroup_change_begin(), so * might no longer be a valid cgroup pointer. cgroup_attach_task() might * have already changed current->cgroups, allowing the previously * referenced cgroup group to be removed and freed.
@@ -4566,10 +4566,14 @@ static const struct file_operations proc_cgroupstats_operations = { */ void cgroup_fork(struct task_struct *child) { - task_lock(current); + /* + * We don't need to task_lock() current because current->cgroups + * can't be changed concurrently here. The parent obviously hasn't + * exited and called cgroup_exit(), and we are synchronized against + * cgroup migration through threadgroup_change_begin(). + */ child->cgroups = current->cgroups; get_css_set(child->cgroups); - task_unlock(current); INIT_LIST_HEAD(&child->cg_list); }
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1.7.5.4