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

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Message-ID: <CAJd=RBAh-GzsfMiViGzKMeDV+G01K_OHZQHJ=amnp0trVhMABQ@mail.gmail.com>
Date:	Thu, 1 Mar 2012 20:48:21 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Li Zefan <lizf@...fujitsu.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

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?

-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);
>  }
>