linux-kernel - Re: [PATCH v2 2/3] cgroup: revise how we re-populate root directory

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Message-ID: <4F505F52.9000509@cn.fujitsu.com>
Date:	Fri, 02 Mar 2012 13:49:06 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Hillf Danton <dhillf@...il.com>
CC:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lennart Poettering <mzxreary@...inter.de>,
	Kay Sievers <kay.sievers@...y.org>,
	Hugh Dickins <hughd@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH v2 2/3] cgroup: revise how we re-populate root directory

20:48, Hillf Danton wrote:
> On Thu, Mar 1, 2012 at 2:17 PM, Li Zefan <lizf@...fujitsu.com> wrote:
>>
>> -static void cgroup_clear_directory(struct dentry *dentry)
>> +static void cgroup_clear_directory(struct dentry *dentry, bool remove_all,
>> +                                  unsigned long removed_bits)
>>  {
>> -       struct list_head *node;
>> +       LIST_HEAD(head);
>> +       struct dentry *d, *node;
>>
>>        BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
>> +
>>        spin_lock(&dentry->d_lock);
>> -       node = dentry->d_subdirs.next;
>> -       while (node != &dentry->d_subdirs) {
>> -               struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
>> +       list_for_each_entry_safe(d, node, &dentry->d_subdirs, d_u.d_child) {
>> +               struct cftype *cft = d->d_fsdata;
>> +
>> +               if (!remove_all && cft->subsys &&
>> +                   !test_bit(cft->subsys->subsys_id, &removed_bits))
>> +                       continue;
>>
>>                spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
>> -               list_del_init(node);
>> +               list_move(&d->d_u.d_child, &head);
>>                if (d->d_inode) {
>>                        /* This should never be called on a cgroup
>>                         * directory with child cgroups */
>>                        BUG_ON(d->d_inode->i_mode & S_IFDIR);
>>                        dget_dlock(d);
>> -                       spin_unlock(&d->d_lock);
>> -                       spin_unlock(&dentry->d_lock);
>> +               }
>> +               spin_unlock(&d->d_lock);
>> +       }
>> +       spin_unlock(&dentry->d_lock);
>> +
> 
> Safe to process isolated entries without dentry->d_lock held?
> 

no vfs expert, I need to check into the vfs code.

> -hd
> 
>> +       list_for_each_entry_safe(d, node, &head, d_u.d_child) {
>> +               spin_lock(&d->d_lock);
>> +               list_del_init(&d->d_u.d_child);
>> +               spin_unlock(&d->d_lock);
>> +               if (d->d_inode) {
>>                        d_delete(d);
>>                        simple_unlink(dentry->d_inode, d);
>>                        dput(d);
>> -                       spin_lock(&dentry->d_lock);
>> -               } else
>> -                       spin_unlock(&d->d_lock);
>> -               node = dentry->d_subdirs.next;
>> +               }
>>        }
>> -       spin_unlock(&dentry->d_lock);
>>  }
>>
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