On Tue, Jan 27, 2026 at 07:00:39AM +0100, Christoph Hellwig wrote:
> > - if (PTR_ERR(folio) == -ENOENT ||
> > - !(IS_ERR(folio) && !folio_test_uptodate(folio))) {
> > + if (folio == ERR_PTR(-ENOENT) ||
> > + (!IS_ERR(folio) && !folio_test_uptodate(folio))) {
> >
> > (Note that PTR_ERR() shouldn't be used before it's known that the
> > pointer is an error pointer.)
>
> That's new to me, and I can't find anything in the documentation or
> implementation suggesting that. Your example code above also does
> this as does plenty of code in the kernel elsewhere.
Not sure why this is controversial. The documentation for PTR_ERR() is
clear that it's for error pointers:
/**
* PTR_ERR - Extract the error code from an error pointer.
* @ptr: An error pointer.
* Return: The error code within @ptr.
*/
static inline long __must_check PTR_ERR(__force const void *ptr)
{
return (long) ptr;
}
Yes, it's really just a cast, and 'PTR_ERR(folio) == -ENOENT' actually
still works when folio isn't necessarily an error pointer. But normally
it would be written as a pointer comparison as I suggested.
- Eric
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