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References: <cover.1260571675.git.kirill@shutemov.name>
	 <ca59c422b495907678915db636f70a8d029cbf3a.1260571675.git.kirill@shutemov.name>
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Date: Wed, 16 Dec 2009 07:46:46 +0200
Message-ID: <cc557aab0912152146t52dabb7hdbd536e9df4f1ab4@mail.gmail.com>
Subject: Re: [PATCH RFC v2 1/4] cgroup: implement eventfd-based generic API
	for notifications
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Content-Type: text/plain; charset=UTF-8
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Sender: owner-linux-mm@kvack.org
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: containers@lists.linux-foundation.org, linux-mm@kvack.org, Paul Menage <menage@google.com>, Andrew Morton <akpm@linux-foundation.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, Pavel Emelyanov <xemul@openvz.org>, Dan Malek <dan@embeddedalley.com>, Vladislav Buzov <vbuzov@embeddedalley.com>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>, linux-kernel@vger.kernel.org
List-ID: <linux-mm.kvack.org>

On Wed, Dec 16, 2009 at 3:44 AM, Li Zefan <lizf@cn.fujitsu.com> wrote:
> Kirill A. Shutemov wrote:
>> This patch introduces write-only file "cgroup.event_control" in every
>> cgroup.
>>
>> To register new notification handler you need:
>> - create an eventfd;
>> - open a control file to be monitored. Callbacks register_event() and
>> =C2=A0 unregister_event() must be defined for the control file;
>> - write "<event_fd> <control_fd> <args>" to cgroup.event_control.
>> =C2=A0 Interpretation of args is defined by control file implementation;
>>
>> eventfd will be woken up by control file implementation or when the
>> cgroup is removed.
>>
>> To unregister notification handler just close eventfd.
>>
>> If you need notification functionality for a control file you have to
>> implement callbacks register_event() and unregister_event() in the
>> struct cftype.
>>
>> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
>> ---
>> =C2=A0include/linux/cgroup.h | =C2=A0 20 +++++
>> =C2=A0kernel/cgroup.c =C2=A0 =C2=A0 =C2=A0 =C2=A0| =C2=A0215 +++++++++++=
++++++++++++++++++++++++++++++++++++-
>> =C2=A02 files changed, 234 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
>> index 0008dee..7ad3078 100644
>> --- a/include/linux/cgroup.h
>> +++ b/include/linux/cgroup.h
>> @@ -220,6 +220,10 @@ struct cgroup {
>>
>> =C2=A0 =C2=A0 =C2=A0 /* For RCU-protected deletion */
>> =C2=A0 =C2=A0 =C2=A0 struct rcu_head rcu_head;
>> +
>> + =C2=A0 =C2=A0 /* List of events which userspace want to recieve */
>> + =C2=A0 =C2=A0 struct list_head event_list;
>> + =C2=A0 =C2=A0 struct mutex event_list_mutex;
>> =C2=A0};
>>
>> =C2=A0/*
>> @@ -362,6 +366,22 @@ struct cftype {
>> =C2=A0 =C2=A0 =C2=A0 int (*trigger)(struct cgroup *cgrp, unsigned int ev=
ent);
>>
>> =C2=A0 =C2=A0 =C2=A0 int (*release)(struct inode *inode, struct file *fi=
le);
>> +
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* register_event() callback will be used to add ne=
w userspace
>> + =C2=A0 =C2=A0 =C2=A0* waiter for changes related to the cftype. Implem=
ent it if
>> + =C2=A0 =C2=A0 =C2=A0* you want to provide this functionality. Use even=
tfd_signal()
>> + =C2=A0 =C2=A0 =C2=A0* on eventfd to send notification to userspace.
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 int (*register_event)(struct cgroup *cgrp, struct cftype=
 *cft,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
struct eventfd_ctx *eventfd, const char *args);
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* unregister_event() callback will be called when =
userspace
>> + =C2=A0 =C2=A0 =C2=A0* close the eventfd. This callback must be impleme=
nted, if you
>> + =C2=A0 =C2=A0 =C2=A0* provide register_event().
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 int (*unregister_event)(struct cgroup *cgrp, struct cfty=
pe *cft,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
struct eventfd_ctx *eventfd);
>> =C2=A0};
>>
>> =C2=A0struct cgroup_scanner {
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index 0249f4b..f7ec3ca 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -4,6 +4,10 @@
>> =C2=A0 * =C2=A0Based originally on the cpuset system, extracted by Paul =
Menage
>> =C2=A0 * =C2=A0Copyright (C) 2006 Google, Inc
>> =C2=A0 *
>> + * =C2=A0Notifiactions support
>
> s/Notifiactions/Notifications

Thanks.

>> + * =C2=A0Copyright (C) 2009 Nokia Corporation
>> + * =C2=A0Author: Kirill A. Shutemov
>> + *
>> =C2=A0 * =C2=A0Copyright notices from the original cpuset code:
>> =C2=A0 * =C2=A0--------------------------------------------------
>> =C2=A0 * =C2=A0Copyright (C) 2003 BULL SA.
>> @@ -51,6 +55,8 @@
>> =C2=A0#include <linux/pid_namespace.h>
>> =C2=A0#include <linux/idr.h>
>> =C2=A0#include <linux/vmalloc.h> /* TODO: replace with more sophisticate=
d array */
>> +#include <linux/eventfd.h>
>> +#include <linux/poll.h>
>>
>> =C2=A0#include <asm/atomic.h>
>>
>> @@ -146,6 +152,36 @@ struct css_id {
>> =C2=A0 =C2=A0 =C2=A0 unsigned short stack[0]; /* Array of Length (depth+=
1) */
>> =C2=A0};
>>
>> +/*
>> + * cgroup_event represents event which userspace want to recieve.
>
> s/event/events ?

Thanks.

>
>> + */
>> +struct cgroup_event {
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* Cgroup which the event belongs to.
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 struct cgroup *cgrp;
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* Control file which the event associated.
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 struct cftype *cft;
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* eventfd to signal userspace about the event.
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 struct eventfd_ctx *eventfd;
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* Each of these stored in a list by the cgroup.
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 struct list_head list;
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* All fields below needed to unregister event when
>> + =C2=A0 =C2=A0 =C2=A0* userspace closes eventfd.
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 poll_table pt;
>> + =C2=A0 =C2=A0 wait_queue_head_t *wqh;
>> + =C2=A0 =C2=A0 wait_queue_t wait;
>> + =C2=A0 =C2=A0 struct work_struct remove;
>> +};
>
> Please add a blank line here.

Ok.

>> +static void cgroup_event_remove(struct cgroup_event *event);
>>
>> =C2=A0/* The list of hierarchy roots */
>>
>> @@ -734,14 +770,29 @@ static struct inode *cgroup_new_inode(mode_t mode,=
 struct super_block *sb)
>> =C2=A0static int cgroup_call_pre_destroy(struct cgroup *cgrp)
>> =C2=A0{
>> =C2=A0 =C2=A0 =C2=A0 struct cgroup_subsys *ss;
>> + =C2=A0 =C2=A0 struct cgroup_event *event, *tmp;
>> =C2=A0 =C2=A0 =C2=A0 int ret =3D 0;
>>
>> =C2=A0 =C2=A0 =C2=A0 for_each_subsys(cgrp->root, ss)
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (ss->pre_destroy) {
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 ret =3D ss->pre_destroy(ss, cgrp);
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 if (ret)
>> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 break;
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 goto out;
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }
>> +
>> + =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0* Unregister events and notify userspace.
>> + =C2=A0 =C2=A0 =C2=A0* FIXME: How to avoid race with cgroup_event_remov=
e_work()
>> + =C2=A0 =C2=A0 =C2=A0* =C2=A0 =C2=A0 =C2=A0 =C2=A0which runs from workq=
ueue?
>> + =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 mutex_lock(&cgrp->event_list_mutex);
>> + =C2=A0 =C2=A0 list_for_each_entry_safe(event, tmp, &cgrp->event_list, =
list) {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 cgroup_event_remove(event);
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 eventfd_signal(event->eventf=
d, 1);
>
> How can you access event after you kfree()ed it in cgroup_event_remove()?

Nice catch. Thank you.

>> + =C2=A0 =C2=A0 }
>> + =C2=A0 =C2=A0 mutex_unlock(&cgrp->event_list_mutex);
>> +
>> +out:
>> =C2=A0 =C2=A0 =C2=A0 return ret;
>> =C2=A0}
>>
>> @@ -1136,6 +1187,8 @@ static void init_cgroup_housekeeping(struct cgroup=
 *cgrp)
>> =C2=A0 =C2=A0 =C2=A0 INIT_LIST_HEAD(&cgrp->release_list);
>> =C2=A0 =C2=A0 =C2=A0 INIT_LIST_HEAD(&cgrp->pidlists);
>> =C2=A0 =C2=A0 =C2=A0 mutex_init(&cgrp->pidlist_mutex);
>> + =C2=A0 =C2=A0 INIT_LIST_HEAD(&cgrp->event_list);
>> + =C2=A0 =C2=A0 mutex_init(&cgrp->event_list_mutex);
>> =C2=A0}
>>
>> =C2=A0static void init_cgroup_root(struct cgroupfs_root *root)
>> @@ -1935,6 +1988,16 @@ static const struct inode_operations cgroup_dir_i=
node_operations =3D {
>> =C2=A0 =C2=A0 =C2=A0 .rename =3D cgroup_rename,
>> =C2=A0};
>>
>> +/*
>> + * Check if a file is a control file
>> + */
>> +static inline struct cftype *__file_cft(struct file *file)
>> +{
>> + =C2=A0 =C2=A0 if (file->f_dentry->d_inode->i_fop !=3D &cgroup_file_ope=
rations)
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return ERR_PTR(-EINVAL);
>
> I don't think this check is needed.
>
>> + =C2=A0 =C2=A0 return __d_cft(file->f_dentry);
>> +}
>> +
>> =C2=A0static int cgroup_create_file(struct dentry *dentry, mode_t mode,
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 struct super_block *sb)
>> =C2=A0{
>> @@ -2789,6 +2852,151 @@ static int cgroup_write_notify_on_release(struct=
 cgroup *cgrp,
>> =C2=A0 =C2=A0 =C2=A0 return 0;
>> =C2=A0}
>>
>> +static inline void cgroup_event_remove(struct cgroup_event *event)
>> +{
>> + =C2=A0 =C2=A0 struct cgroup *cgrp =3D event->cgrp;
>> +
>> + =C2=A0 =C2=A0 BUG_ON(event->cft->unregister_event(cgrp, event->cft, ev=
ent->eventfd));
>> + =C2=A0 =C2=A0 eventfd_ctx_put(event->eventfd);
>> + =C2=A0 =C2=A0 remove_wait_queue(event->wqh, &event->wait);
>> + =C2=A0 =C2=A0 list_del(&event->list);
>> + =C2=A0 =C2=A0 kfree(event);
>> +}
>> +
>> +static void cgroup_event_remove_work(struct work_struct *work)
>> +{
>> + =C2=A0 =C2=A0 struct cgroup_event *event =3D container_of(work, struct=
 cgroup_event,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
remove);
>> + =C2=A0 =C2=A0 struct cgroup *cgrp =3D event->cgrp;
>> +
>> + =C2=A0 =C2=A0 mutex_lock(&cgrp->event_list_mutex);
>> + =C2=A0 =C2=A0 cgroup_event_remove(event);
>> + =C2=A0 =C2=A0 mutex_unlock(&cgrp->event_list_mutex);
>> +}
>> +
>> +static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 int sync, void *key)
>> +{
>> + =C2=A0 =C2=A0 struct cgroup_event *event =3D container_of(wait,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
struct cgroup_event, wait);
>> + =C2=A0 =C2=A0 unsigned long flags =3D (unsigned long)key;
>> +
>> + =C2=A0 =C2=A0 if (flags & POLLHUP)
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 /*
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* This function called=
 with spinlock taken, but
>
> s/called/is called/ ?

Ok.

>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* cgroup_event_remove(=
) may sleep, so we have
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* to run it in a workq=
ueue.
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0*/
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 schedule_work(&event->remove=
);
>
> Please use:
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0if (...) {
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0...
> =C2=A0 =C2=A0 =C2=A0 =C2=A0}

Ok.

>> +
>> + =C2=A0 =C2=A0 return 0;
>> +}
>> +
>> +static void cgroup_event_ptable_queue_proc(struct file *file,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 wait_queue_head_t *wqh, poll=
_table *pt)
>> +{
>> + =C2=A0 =C2=A0 struct cgroup_event *event =3D container_of(pt,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
struct cgroup_event, pt);
>> +
>> + =C2=A0 =C2=A0 event->wqh =3D wqh;
>> + =C2=A0 =C2=A0 add_wait_queue(wqh, &event->wait);
>> +}
>> +
>> +static int cgroup_write_event_control(struct cgroup *cont, struct cftyp=
e *cft,
>
> Please consistently use "cgrp"

Ok.

>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 const char *buffer)
>> +{
>> + =C2=A0 =C2=A0 struct cgroup_event *event =3D NULL;
>> + =C2=A0 =C2=A0 unsigned int efd, cfd;
>> + =C2=A0 =C2=A0 struct file *efile =3D NULL;
>> + =C2=A0 =C2=A0 struct file *cfile =3D NULL;
>> + =C2=A0 =C2=A0 char *endp;
>> + =C2=A0 =C2=A0 int ret;
>> +
>> + =C2=A0 =C2=A0 efd =3D simple_strtoul(buffer, &endp, 10);
>> + =C2=A0 =C2=A0 if (*endp !=3D ' ')
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return -EINVAL;
>> + =C2=A0 =C2=A0 buffer =3D endp + 1;
>> +
>> + =C2=A0 =C2=A0 cfd =3D simple_strtoul(buffer, &endp, 10);
>> + =C2=A0 =C2=A0 if ((*endp !=3D ' ') && (*endp !=3D '\0'))
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return -EINVAL;
>> + =C2=A0 =C2=A0 buffer =3D endp + 1;
>> +
>> + =C2=A0 =C2=A0 event =3D kzalloc(sizeof(*event), GFP_KERNEL);
>> + =C2=A0 =C2=A0 if (!event)
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return -ENOMEM;
>> + =C2=A0 =C2=A0 event->cgrp =3D cont;
>> + =C2=A0 =C2=A0 INIT_LIST_HEAD(&event->list);
>> + =C2=A0 =C2=A0 init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_=
proc);
>> + =C2=A0 =C2=A0 init_waitqueue_func_entry(&event->wait, cgroup_event_wak=
e);
>> + =C2=A0 =C2=A0 INIT_WORK(&event->remove, cgroup_event_remove_work);
>> +
>> + =C2=A0 =C2=A0 efile =3D eventfd_fget(efd);
>> + =C2=A0 =C2=A0 if (IS_ERR(efile)) {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ret =3D PTR_ERR(efile);
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> + =C2=A0 =C2=A0 }
>> +
>> + =C2=A0 =C2=A0 event->eventfd =3D eventfd_ctx_fileget(efile);
>> + =C2=A0 =C2=A0 if (IS_ERR(event->eventfd)) {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ret =3D PTR_ERR(event->event=
fd);
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> + =C2=A0 =C2=A0 }
>> +
>> + =C2=A0 =C2=A0 cfile =3D fget(cfd);
>> + =C2=A0 =C2=A0 if (!cfile) {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ret =3D -EBADF;
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> + =C2=A0 =C2=A0 }
>> +
>> + =C2=A0 =C2=A0 /* the process need read permission on control file */
>> + =C2=A0 =C2=A0 ret =3D file_permission(cfile, MAY_READ);
>> + =C2=A0 =C2=A0 if (ret < 0)
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> +
>> + =C2=A0 =C2=A0 event->cft =3D __file_cft(cfile);
>> + =C2=A0 =C2=A0 if (IS_ERR(event->cft)) {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ret =3D PTR_ERR(event->cft);
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> + =C2=A0 =C2=A0 }
>> +
>> + =C2=A0 =C2=A0 if (!event->cft->register_event || !event->cft->unregist=
er_event) {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ret =3D -EINVAL;
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> + =C2=A0 =C2=A0 }
>> +
>> + =C2=A0 =C2=A0 ret =3D event->cft->register_event(cont, event->cft,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
event->eventfd, buffer);
>> + =C2=A0 =C2=A0 if (ret)
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto fail;
>> +
>> + =C2=A0 =C2=A0 efile->f_op->poll(efile, &event->pt);
>> +
>> + =C2=A0 =C2=A0 mutex_lock(&cont->event_list_mutex);
>> + =C2=A0 =C2=A0 list_add(&event->list, &cont->event_list);
>> + =C2=A0 =C2=A0 mutex_unlock(&cont->event_list_mutex);
>> +
>> + =C2=A0 =C2=A0 fput(cfile);
>> + =C2=A0 =C2=A0 fput(efile);
>> +
>> + =C2=A0 =C2=A0 return 0;
>> +
>> +fail:
>> + =C2=A0 =C2=A0 if (!IS_ERR(cfile))
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 fput(cfile);
>> +
>> + =C2=A0 =C2=A0 if (event && event->eventfd && !IS_ERR(event->eventfd))
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 eventfd_ctx_put(event->event=
fd);
>> +
>> + =C2=A0 =C2=A0 if (!IS_ERR(efile))
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 fput(efile);
>> +
>> + =C2=A0 =C2=A0 if (event)
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 kfree(event);
>
> kfree(NULL) is ok

Ok.

>> +
>> + =C2=A0 =C2=A0 return ret;
>> +}
>> +
>> =C2=A0/*
>> =C2=A0 * for the common functions, 'private' gives the type of file
>> =C2=A0 */
>> @@ -2814,6 +3022,11 @@ static struct cftype files[] =3D {
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .read_u64 =3D cgroup_re=
ad_notify_on_release,
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .write_u64 =3D cgroup_w=
rite_notify_on_release,
>> =C2=A0 =C2=A0 =C2=A0 },
>> + =C2=A0 =C2=A0 {
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .name =3D CGROUP_FILE_GENERI=
C_PREFIX "event_control",
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .write_string =3D cgroup_wri=
te_event_control,
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .mode =3D S_IWUGO,
>
> We want this file to be writable to everyone ?

Yes. We check permission of the file which we want to track.

>> + =C2=A0 =C2=A0 },
>> =C2=A0};
>>
>> =C2=A0static struct cftype cft_release_agent =3D {
>

Thank you.

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