linux-kernel - Re: [PATCH] crypto/async_pq: use __free_page() instead of put

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Date:	Fri, 4 Mar 2016 10:06:45 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Arnd Bergmann <arnd@...db.de>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	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>,
	"David S. Miller" <davem@...emloft.net>,
	NeilBrown <neilb@...e.com>,
	Markus Stockhausen <stockhausen@...logia.de>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto/async_pq: use __free_page() instead of put_page()

On 02/29/2016 10:33 AM, Arnd Bergmann wrote:
> 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
> 
> From a cursory look at that this driver, it seems that it may be
> doing the wrong thing here anyway, as the page gets allocated
> using 'alloc_page()', and should be freed using '__free_page()'
> rather than 'put_page()'.
> 
> With this patch, I no longer get any other build errors from the
> page_ref patch, so hopefully we can assume that it's always wrong
> to call any of those functions from __exit code, and that no other
> driver does it.

Hopefully that's true. If any such driver was leaking references to
those pages, so the put_page() didn't actually result in freeing, the
explicit __free_page should catch this via built-in checks.

> Fixes: 0f80830dd044 ("mm/page_ref: add tracepoint to track down page reference manipulation")

Since it's in mmotm which is quilt-based, the commit hash from -next is
not stable.

> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  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..08b3ac68952b 100644
> --- a/crypto/async_tx/async_pq.c
> +++ b/crypto/async_tx/async_pq.c
> @@ -444,7 +444,7 @@ static int __init async_pq_init(void)
>  
>  static void __exit async_pq_exit(void)
>  {
> -	put_page(pq_scribble_page);
> +	__free_page(pq_scribble_page);
>  }
>  
>  module_init(async_pq_init);
>