clone3: allow spawning processes into cgroups

This adds support for creating a process in a different cgroup than its
parent. Callers can limit and account processes and threads right from
the moment they are spawned:
- A service manager can directly spawn new services into dedicated
  cgroups.
- A process can be directly created in a frozen cgroup and will be
  frozen as well.
- The initial accounting jitter experienced by process supervisors and
  daemons is eliminated with this.
- Threaded applications or even thread implementations can choose to
  create a specific cgroup layout where each thread is spawned
  directly into a dedicated cgroup.

This feature is limited to the unified hierarchy. Callers need to pass
a directory file descriptor for the target cgroup. The caller can
choose to pass an O_PATH file descriptor. All usual migration
restrictions apply, i.e. there can be no processes in inner nodes. In
general, creating a process directly in a target cgroup adheres to all
migration restrictions.

One of the biggest advantages of this feature is that CLONE_INTO_GROUP does
not need to grab the write side of the cgroup cgroup_threadgroup_rwsem.
This global lock makes moving tasks/threads around super expensive. With
clone3() this lock is avoided.

Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: cgroups@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 14 insertions, 6 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f1219b927817..4598e4da6b1b 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -27,6 +27,8 @@
 
 #include <linux/cgroup-defs.h>
 
+struct kernel_clone_args;
+
 #ifdef CONFIG_CGROUPS
 
 /*
@@ -119,9 +121,12 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		     struct pid *pid, struct task_struct *tsk);
 
 void cgroup_fork(struct task_struct *p);
-extern int cgroup_can_fork(struct task_struct *p);
-extern void cgroup_cancel_fork(struct task_struct *p);
-extern void cgroup_post_fork(struct task_struct *p);
+extern int cgroup_can_fork(struct task_struct *p,
+			   struct kernel_clone_args *kargs);
+extern void cgroup_cancel_fork(struct task_struct *p,
+			       struct kernel_clone_args *kargs);
+extern void cgroup_post_fork(struct task_struct *p,
+			     struct kernel_clone_args *kargs);
 void cgroup_exit(struct task_struct *p);
 void cgroup_release(struct task_struct *p);
 void cgroup_free(struct task_struct *p);
@@ -705,9 +710,12 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
 				    struct dentry *dentry) { return -EINVAL; }
 
 static inline void cgroup_fork(struct task_struct *p) {}
-static inline int cgroup_can_fork(struct task_struct *p) { return 0; }
-static inline void cgroup_cancel_fork(struct task_struct *p) {}
-static inline void cgroup_post_fork(struct task_struct *p) {}
+static inline int cgroup_can_fork(struct task_struct *p,
+				  struct kernel_clone_args *kargs) { return 0; }
+static inline void cgroup_cancel_fork(struct task_struct *p,
+				      struct kernel_clone_args *kargs) {}
+static inline void cgroup_post_fork(struct task_struct *p,
+				    struct kernel_clone_args *kargs) {}
 static inline void cgroup_exit(struct task_struct *p) {}
 static inline void cgroup_release(struct task_struct *p) {}
 static inline void cgroup_free(struct task_struct *p) {}