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

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>
Cc: <stable@vger.kernel.org> # 4.4+ prerequisite for the next patch

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 3e39ae5..5b17de6 100644 (file)
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -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);

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index fea160e..85a868c 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -137,8 +137,6 @@ static inline void set_mems_allowed(nodemask_t nodemask)
        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_retry(unsigned int seq)
        return false;
 }
 
-static inline void cpuset_post_attach_flush(void)
-{
-}
-
 #endif /* !CONFIG_CPUSETS */
 
 #endif /* _LINUX_CPUSET_H */

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 671dc05..909a7d3 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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:
        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;
 }
 

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 00ab5c2..1902956 100644 (file)
--- 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_struct *mm, const nodemask_t *from,
        }
 }
 
-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     = true,