linux-kernel - Re: [PATCH] [RFC] mm/page_ref, crypto/async_pq: don't put_page from _

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Date:	Mon, 29 Feb 2016 16:40:02 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-arm-kernel@...ts.infradead.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] mm/page_ref, crypto/async_pq: don't put_page from __exit

2016-02-29 6:57 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> 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@...db.de>
> 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.