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

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 <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
parent bcc981e9

include/linux/cgroup-defs.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

include/linux/cpuset.h

+0 −6
Original line number Diff line number Diff line
@@ -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 */

kernel/cgroup.c

+5 −2
Original line number Diff line number Diff line
@@ -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 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf, 
	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;

}

kernel/cpuset.c

+2 −2
Original line number Diff line number Diff line
@@ -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,