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SubjectRe: [PATCH -mm] swsusp: userland interface (rev 2)
Date
Hi,

On Wednesday, 25 January 2006 13:18, Pavel Machek wrote:
> > > > + case SNAPSHOT_ATOMIC_RESTORE:
> > > > + if (data->mode != O_WRONLY || !data->frozen ||
> > > > + !snapshot_image_loaded(&data->handle)) {
> > > > + error = -EPERM;
> > > > + break;
> > > > + }
> > > > + down(&pm_sem);
> > > > + pm_prepare_console();
> > > > + error = device_suspend(PMSG_FREEZE);
> > > > + if (!error) {
> > > > + mb();
> > > > + error = swsusp_resume();
> > > > + device_resume();
> > > > + }
> > >
> > > whee, what does the mystery barrier do? It'd be nice to comment this
> > > (please always comment open-coded barriers).
> >
> > Pavel should know. ;-)
>
> Pavel does not known. That memory barrier should be part of assembly
> parts, anyway, and AFAIK it is. Should be safe to kill.

OK

> > > > + case SNAPSHOT_GET_SWAP_PAGE:
> > > > + if (!access_ok(VERIFY_WRITE, (unsigned long __user *)arg, _IOC_SIZE(cmd))) {
> > > > + error = -EINVAL;
> > > > + break;
> > > > + }
> > >
> > > Why do we need an access_ok() here?
> >
> > Because we use __put_user() down the road?
> >
> > The problem is if the address is wrong we should not try to call
> > alloc_swap_page() at all. If we did, we wouldn't be able to return the result
> > and we would leak a swap page.
>
> I think you need to watch for failing put_user and free the page at
> that point. Anything else is racy as __put_user() may fail.

The page will be freed anyway when the device is closed (I was wrong
saying it would be "leaked"), so I think I'll just use put_user().

Greetings,
Rafael
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