Hi, Yamamoto-san.
Thank you for your comment.
On Fri, 4 Jul 2008 15:54:31 +0900 (JST), yamamoto@xxxxxxxxxxxxx (YAMAMOTO Takashi) wrote:
> hi,
>
> > +/*
> > + * uncharge all the entries that are charged to the group.
> > + */
> > +void __swap_cgroup_force_empty(struct mem_cgroup *mem)
> > +{
> > + struct swap_info_struct *p;
> > + int type;
> > +
> > + spin_lock(&swap_lock);
> > + for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
> > + p = swap_info + type;
> > +
> > + if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
> > + unsigned int i = 0;
> > +
> > + spin_unlock(&swap_lock);
>
> what prevents the device from being swapoff'ed while you drop swap_lock?
>
Nothing.
After searching the entry to be uncharged(find_next_to_unuse below),
I recheck under swap_lock whether the entry is charged to the group.
Even if the device is swapoff'ed, swap_off must have uncharged the entry,
so I don't think it's needed anyway.
> YAMAMOTO Takashi
>
> > + while ((i = find_next_to_unuse(p, i, mem)) != 0) {
> > + spin_lock(&swap_lock);
> > + if (p->swap_map[i] && p->memcg[i] == mem)
Ah, I think it should be added !p->swap_map to check the device has not
been swapoff'ed.
Thanks,
Daisuke Nishimura.
> > + swap_cgroup_uncharge(p, i);
> > + spin_unlock(&swap_lock);
> > + }
> > + spin_lock(&swap_lock);
> > + }
> > + }
> > + spin_unlock(&swap_lock);
> > +
> > + return;
> > +}
> > #endif
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