On Mon, 22 Dec 2008, Greg KH wrote:
> On Tue, Dec 23, 2008 at 07:01:59AM +0100, Julia Lawall wrote:
> > On Mon, 22 Dec 2008, Greg KH wrote:
> >
> > > On Fri, Dec 19, 2008 at 06:56:46PM +0100, Julia Lawall wrote:
> > > > Considering code such as the following (drivers/acpi/osl.c):
> > > >
> > > > struct acpi_os_dpc *dpc = container_of(work, struct acpi_os_dpc, work);
> > > > if (!dpc) {
> > > > printk(KERN_ERR PREFIX "Invalid (NULL) context\n");
> > > > return;
> > > > }
> > > >
> > > > Is it very likely that container_of can return NULL? Container_of
> > > > computes an offset from a pointer, so I have the impression that if given
> > > > a NULL value it would normally return a negative number (or a very large
> > > > positive one, depending on how it is interpreted).
> > >
> > > You are correct, that check will never happen, and should be removed.
> >
> > Actually, someone else pointed out that one could call the function with
> > &x->fld, and if x is NULL, then container_of(&x->fld,...) would go back
> > down to NULL. I haven't looked at the call sites though to see if that
> > can happen.
>
> No, if you were to evaluate x->fld, you would oops :)
&x->fld doesn't oops, though. It just adds the offset of the field fld to
x.
julia
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