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Commit 2468c723 authored by Daisuke Nishimura's avatar Daisuke Nishimura Committed by Linus Torvalds
Browse files

cgroup: introduce cancel_attach() 



Add cancel_attach() operation to struct cgroup_subsys.  cancel_attach()
can be used when can_attach() operation prepares something for the subsys,
but we should rollback what can_attach() operation has prepared if attach
task fails after we've succeeded in can_attach().

Signed-off-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Reviewed-by: default avatarPaul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5ce9f07b

Documentation/cgroups/cgroups.txt

+12 −1
Original line number Diff line number Diff line
@@ -536,10 +536,21 @@ returns an error, this will abort the attach operation. If a NULL 
task is passed, then a successful result indicates that *any*

unspecified task can be moved into the cgroup. Note that this isn't

called on a fork. If this method returns 0 (success) then this should

remain valid while the caller holds cgroup_mutex. If threadgroup is

remain valid while the caller holds cgroup_mutex and it is ensured that either

attach() or cancel_attach() will be called in future. If threadgroup is

true, then a successful result indicates that all threads in the given

thread's threadgroup can be moved together.



void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,

	       struct task_struct *task, bool threadgroup)

(cgroup_mutex held by caller)



Called when a task attach operation has failed after can_attach() has succeeded.

A subsystem whose can_attach() has some side-effects should provide this

function, so that the subsytem can implement a rollback. If not, not necessary.

This will be called only about subsystems whose can_attach() operation have

succeeded.



void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,

	    struct cgroup *old_cgrp, struct task_struct *task,

	    bool threadgroup)

include/linux/cgroup.h

+2 −0
Original line number Diff line number Diff line
@@ -428,6 +428,8 @@ struct cgroup_subsys { 
	void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);

	int (*can_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,

			  struct task_struct *tsk, bool threadgroup);

	void (*cancel_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,

			  struct task_struct *tsk, bool threadgroup);

	void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,

			struct cgroup *old_cgrp, struct task_struct *tsk,

			bool threadgroup);

kernel/cgroup.c

+33 −7
Original line number Diff line number Diff line
@@ -1554,7 +1554,7 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) 
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)

{

	int retval = 0;

	struct cgroup_subsys *ss;

	struct cgroup_subsys *ss, *failed_ss = NULL;

	struct cgroup *oldcgrp;

	struct css_set *cg;

	struct css_set *newcg;
@@ -1568,8 +1568,16 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk) 
	for_each_subsys(root, ss) {

		if (ss->can_attach) {

			retval = ss->can_attach(ss, cgrp, tsk, false);

			if (retval)

				return retval;

			if (retval) {

				/*

				 * Remember on which subsystem the can_attach()

				 * failed, so that we only call cancel_attach()

				 * against the subsystems whose can_attach()

				 * succeeded. (See below)

				 */

				failed_ss = ss;

				goto out;

			}

		}

	}
@@ -1583,14 +1591,17 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk) 
	 */

	newcg = find_css_set(cg, cgrp);

	put_css_set(cg);

	if (!newcg)

		return -ENOMEM;

	if (!newcg) {

		retval = -ENOMEM;

		goto out;

	}



	task_lock(tsk);

	if (tsk->flags & PF_EXITING) {

		task_unlock(tsk);

		put_css_set(newcg);

		return -ESRCH;

		retval = -ESRCH;

		goto out;

	}

	rcu_assign_pointer(tsk->cgroups, newcg);

	task_unlock(tsk);
@@ -1616,7 +1627,22 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk) 
	 * is no longer empty.

	 */

	cgroup_wakeup_rmdir_waiter(cgrp);

	return 0;

out:

	if (retval) {

		for_each_subsys(root, ss) {

			if (ss == failed_ss)

				/*

				 * This subsystem was the one that failed the

				 * can_attach() check earlier, so we don't need

				 * to call cancel_attach() against it or any

				 * remaining subsystems.

				 */

				break;

			if (ss->cancel_attach)

				ss->cancel_attach(ss, cgrp, tsk, false);

		}

	}

	return retval;

}



/*