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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: anfei <anfei.zhou@gmail.com>
Subject: Re: cache alias in mmap + write
Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, linux@arm.linux.org.uk, jamie@shareable.org
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Date: Wed, 20 Jan 2010 18:10:11 +0900 (JST)
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Hello,

> diff --git a/mm/filemap.c b/mm/filemap.c
> index 96ac6b0..07056fb 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2196,6 +2196,9 @@ again:
>  		if (unlikely(status))
>  			break;
>  
> +		if (mapping_writably_mapped(mapping))
> +			flush_dcache_page(page);
> +
>  		pagefault_disable();
>  		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
>  		pagefault_enable();

I'm not sure ARM cache coherency model. but I guess correct patch is here.

+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
 		pagefault_disable();
 		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
 		pagefault_enable();
-		flush_dcache_page(page);


Why do we need to call flush_dcache_page() twice?