On Tue, 15 Sep 2020 at 10:05, Herbert Xu <herb...@gondor.apana.org.au> wrote:
>
> On Mon, Sep 14, 2020 at 11:55:53PM -0700, Linus Torvalds wrote:
> >
> > Maybe we could hide it behind a debug option, at least.
> >
> > Or, alterantively, introduce a new "debug_preempt_count" that doesn't
> > actually disable preemption, but warns about actual sleeping
> > operations..
>
> I'm more worried about existing users of kmap_atomic relying on
> the preemption disabling semantics. Short of someone checking
> on every single instance (and that would include derived cases
> such as all users of sg miter), I think the safer option is to
> create something brand new and then migrate the existing users
> to it. Something like
>
> static inline void *kmap_atomic_ifhigh(struct page *page)
> {
> if (PageHighMem(page))
> return kmap_atomic(page);
> return page_address(page);
> }
>
> static inline void kunmap_atomic_ifhigh(struct page *page, void *addr)
> {
> if (PageHighMem(page))
> kunmap_atomic(addr);
> }
>
But we would still need to check all users of SG miter before we could
move it to this interface.
