Re: [PATCH] [RFC] mm/page_ref, crypto/async_pq: don't put_page from __exit

[Joonsoo Kim]

2016-02-29 6:57 GMT+09:00 Arnd Bergmann <arnd@xxxxxxxx>:
> The addition of tracepoints to the page reference tracking had an
> unfortunate side-effect in at least one driver that calls put_page
> from its exit function, resulting in a link error:
>
> `.exit.text' referenced in section `__jump_table' of crypto/built-in.o: defined in discarded section `.exit.text' of crypto/built-in.o
>
> I could not come up with a nice solution that ignores __jump_table
> entries in discarded code, so we probably now have to treat this
> as something a driver is not allowed to do. Removing the __exit
> annotation avoids the problem in this particular driver, but the
> same problem could come back any time in other code.
>
> On a related problem regarding the runtime patching for SMP
> operations on ARM uniprocessor systems, we resorted to not
> drop the .exit section at link time, but that doesn't seem
> appropriate here.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> Fixes: 0f80830dd044 ("mm/page_ref: add tracepoint to track down page reference manipulation")
> ---
>  crypto/async_tx/async_pq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
> index c0748bbd4c08..be167145aa55 100644
> --- a/crypto/async_tx/async_pq.c
> +++ b/crypto/async_tx/async_pq.c
> @@ -442,7 +442,7 @@ static int __init async_pq_init(void)
>         return -ENOMEM;
>  }
>
> -static void __exit async_pq_exit(void)
> +static void async_pq_exit(void)
>  {
>         put_page(pq_scribble_page);
>  }

Hello, Arnd.

I think that we can avoid this error by using __free_page().
It would not be inlined so calling it would have no problem.

Could you test it, please?

Thanks.