Commit 5cf1cacb authored by Tejun Heo's avatar Tejun Heo

cgroup, cpuset: replace cpuset_post_attach_flush() with cgroup_subsys->post_attach callback

Since e93ad19d ("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: default avatarTejun Heo <>
Cc: Li Zefan <>
Cc: Johannes Weiner <>
Cc: Michal Hocko <>
Cc: <> # 4.4+ prerequisite for the next patch
parent bcc981e9
......@@ -444,6 +444,7 @@ 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);
......@@ -137,8 +137,6 @@ static inline void set_mems_allowed(nodemask_t nodemask)
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_retry(unsigned int seq)
return false;
static inline void cpuset_post_attach_flush(void)
#endif /* !CONFIG_CPUSETS */
#endif /* _LINUX_CPUSET_H */
......@@ -2825,9 +2825,10 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
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;
......@@ -2875,8 +2876,10 @@ out_unlock_rcu:
for_each_subsys(ss, ssid)
if (ss->post_attach)
return ret ?: nbytes;
......@@ -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_struct *mm, const nodemask_t *from,
void cpuset_post_attach_flush(void)
static void cpuset_post_attach(void)
......@@ -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 = true,
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