[PATCH 4.5 130/200] cgroup, cpuset: replace cpuset_post_attach_flush() with cgroup_subsys->post_attach callback

Greg Kroah-Hartman
2016-05-03T00:44:28Z

From: Tejun Heo <tj@kernel.org>

commit 5cf1cacb49aee39c3e02ae87068fc3c6430659b0 upstream.

Since e93ad19d0564 ("cpuset: make mm migration asynchronous"), cpuset
kicks off asynchronous NUMA node migration if necessary during task
migration and flushes it from cpuset_post_attach_flush() which is
called at the end of __cgroup_procs_write(). This is to avoid
performing migration with cgroup_threadgroup_rwsem write-locked which
can lead to deadlock through dependency on kworker creation.

memcg has a similar issue with charge moving, so let's convert it to
an official callback rather than the current one-off cpuset specific
function. This patch adds cgroup_subsys->post_attach callback and
makes cpuset register cpuset_post_attach_flush() as its ->post_attach.

The conversion is mostly one-to-one except that the new callback is
called under cgroup_mutex. This is to guarantee that no other
migration operations are started before ->post_attach callbacks are
finished. cgroup_mutex is one of the outermost mutex in the system
and has never been and shouldn't be a problem. We can add specialized
synchronization around __cgroup_procs_write() but I don't think
there's any noticeable benefit.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/cgroup-defs.h | 1 +
include/linux/cpuset.h | 6 ------
kernel/cgroup.c | 7 +++++--
kernel/cpuset.c | 4 ++--
4 files changed, 8 insertions(+), 10 deletions(-)

--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -442,6 +442,7 @@ struct cgroup_subsys {
int (*can_attach)(struct cgroup_taskset *tset);
void (*cancel_attach)(struct cgroup_taskset *tset);
void (*attach)(struct cgroup_taskset *tset);
+ void (*post_attach)(void);
int (*can_fork)(struct task_struct *task);
void (*cancel_fork)(struct task_struct *task);
void (*fork)(struct task_struct *task);
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -137,8 +137,6 @@ static inline void set_mems_allowed(node
task_unlock(current);
}

-extern void cpuset_post_attach_flush(void);
-
#else /* !CONFIG_CPUSETS */

static inline bool cpusets_enabled(void) { return false; }
@@ -245,10 +243,6 @@ static inline bool read_mems_allowed_ret
return false;
}

-static inline void cpuset_post_attach_flush(void)
-{
-}
-
#endif /* !CONFIG_CPUSETS */

#endif /* _LINUX_CPUSET_H */
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2697,9 +2697,10 @@ static ssize_t __cgroup_procs_write(stru
size_t nbytes, loff_t off, bool threadgroup)
{
struct task_struct *tsk;
+ struct cgroup_subsys *ss;
struct cgroup *cgrp;
pid_t pid;
- int ret;
+ int ssid, ret;

if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
return -EINVAL;
@@ -2747,8 +2748,10 @@ out_unlock_rcu:
rcu_read_unlock();
out_unlock_threadgroup:
percpu_up_write(&cgroup_threadgroup_rwsem);
+ for_each_subsys(ss, ssid)
+ if (ss->post_attach)
+ ss->post_attach();
cgroup_kn_unlock(of->kn);
- cpuset_post_attach_flush();
return ret ?: nbytes;
}

--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -58,7 +58,6 @@
#include <asm/uaccess.h>
#include <linux/atomic.h>
#include <linux/mutex.h>
-#include <linux/workqueue.h>
#include <linux/cgroup.h>
#include <linux/wait.h>

@@ -1016,7 +1015,7 @@ static void cpuset_migrate_mm(struct mm_
}
}

-void cpuset_post_attach_flush(void)
+static void cpuset_post_attach(void)
{
flush_workqueue(cpuset_migrate_mm_wq);
}
@@ -2087,6 +2086,7 @@ struct cgroup_subsys cpuset_cgrp_subsys
.can_attach = cpuset_can_attach,
.cancel_attach = cpuset_cancel_attach,
.attach = cpuset_attach,
+ .post_attach = cpuset_post_attach,
.bind = cpuset_bind,
.legacy_cftypes = files,
.early_init = 1,