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

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

[Arnd Bergmann]

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@arndb.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);
 }
-- 
2.7.0

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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@arndb.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@arndb.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.

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

[Arnd Bergmann]

On Monday 29 February 2016 16:40:02 Joonsoo Kim wrote:
> 
> 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?

Yes, I suspect the driver should have done that anyway, new patch
under way.

	Arnd

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