On 6/1/05, Alan Stern <[EMAIL PROTECTED]> wrote:
> On Wed, 1 Jun 2005, Dmitry Torokhov wrote:
>
> > > +static ssize_t show_tabletSize(struct device *dev, char *buf)
> > > +{
> > > + struct usb_acecad *acecad = dev_get_drvdata(dev);
> > > +
> > > + if (acecad == NULL)
> > > + return 0;
> >
> > This check - is it really needed? Attributes are deleted in
> > disconnect... Wait, this needs locking because if someone happens to
> > read one of the attributes while usb_acecad_disconnect is running you
> > may end up accessing just freed memory, no?
>
> No.
>
> Attributes are complex things. When an attribute is opened the sysfs code
> does kobject_get on the underlying object. The release method won't get
> called, and hence the memory won't get freed, until the attribute is
> closed.
>
> On the other hand, remove methods typically do call dev_set_drvdata(dev,
> NULL). Thus a read-during-disconnect might very well end up with acecad
> == NULL, and so the check above is necessary.
>
OK, consider this:
CPU1: CPU2
if (acecad == NULL) // fails
usb_set_intfdata(intf, NULL);
...
kfree(acecad);
sprintf(... acecad->blah) -> oops
Unprotected check does not help and might as well be removed, with
proper locking in place it is not needed either.
--
Dmitry
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