[PATCH 2/2 v3] cgroup: Drop task_lock(parent) on cgroup_fork()
From: Frederic Weisbecker <hidden>
Date: 2011-12-21 19:03:37
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 | 23 +++++++++++++++++------ 1 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 24f6d6f..4936d88 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c@@ -4556,20 +4556,31 @@ 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 - * 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. + * it was not made under the protection of RCU, cgroup_mutex or + * threadgroup_change_begin(), so it 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. + * + * Outside the pointer validity we also need to process the css_set + * inheritance between threadgoup_change_begin() and + * threadgoup_change_end(), this way there is no leak in any process + * wide migration performed by cgroup_attach_proc() that could otherwise + * miss a thread because it is too early or too late in the fork stage. * * At the point that cgroup_fork() is called, 'current' is the parent * task, and the passed argument 'child' points to the child task. */ 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