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SubjectRe: [PATCH, v4] hwmon: coretemp: use list instead of fixed size array for temp data
On Wed, May 09, 2012 at 10:09:06AM +0300, Kirill A. Shutemov wrote:
> On Tue, May 08, 2012 at 09:39:40AM -0700, Guenter Roeck wrote:
> > On Tue, 2012-05-08 at 06:49 -0400, Kirill A. Shutemov wrote:
> > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > >
> > > Let's rework code to allow arbitrary number of cores on a CPU, not
> > > limited by hardcoded array size.
> > >
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > > ---
> > > v4:
> > > - address issues pointed by Guenter Roeck;
> > > v3:
> > > - drop redundant refcounting and checks;
> > > v2:
> > > - fix NULL pointer dereference. Thanks to R, Durgadoss;
> > > - use mutex instead of spinlock for list locking.
> > > ---
> >
> > Hi Kirill,
> >
> > unfortunately now we have another race condition :(. See below ...
>
> Ughh..
>
> > > @@ -557,11 +579,22 @@ exit_free:
> > > static int __devexit coretemp_remove(struct platform_device *pdev)
> > > {
> > > struct platform_data *pdata = platform_get_drvdata(pdev);
> > > - int i;
> > > + struct temp_data *tdata;
> > >
> > > - for (i = MAX_CORE_DATA - 1; i >= 0; --i)
> > > - if (pdata->core_data[i])
> > > - coretemp_remove_core(pdata, &pdev->dev, i);
> > > + for (;;) {
> > > + mutex_lock(&pdata->temp_data_lock);
> > > + if (!list_empty(&pdata->temp_data_list)) {
> > > + tdata = list_first_entry(&pdata->temp_data_list,
> > > + struct temp_data, list);
> > > + list_del(&tdata->list);
> > > + } else
> > > + tdata = NULL;
> > > + mutex_unlock(&pdata->temp_data_lock);
> > > +
> > > + if (!tdata)
> > > + break;
> > > + coretemp_remove_core(tdata, &pdev->dev);
> > > + }
> > >
> > Unfortunately, that results in a race condition, since the tdata list
> > entry is gone before the attribute file is deleted.
> >
> > I think you can still use list_for_each_entry_safe, only outside the
> > mutex, and remove the list entry at the end of coretemp_remove_core()

I haven't got how list_for_each_entry_safe() will be really safe without
the lock.

> > after deleting the attribute file. Just keep the code as it was, and
> > remove the list entry (mutex-protected) where core_data[] was set to
> > NULL.
>
> I think
>
> if (tdata)
> return -ENODEV;
>
> in show methods will fix the issue. Right?

It won't. Stupid me.

But the check + kref seems will work...

--
Kirill A. Shutemov
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