[PATCH] bug:roundup_pow_of_two(size) will return 0 when size > 2^63 because of overflow problem. fix:when size > max, return max. (when newsize > max will return max originally)

[PATCH] bug:roundup_pow_of_two(size) will return 0 when size > 2^63 because of overflow problem. fix:when size > max, return max. (when newsize > max will return max originally)

[? ??]

Signed-off-by: LongPing.WEI <weilongpingshu@hotmail.com>
---
 mm/readahead.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index c4ca702..4941f04 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -248,7 +248,12 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
  */
 static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
 {
-	unsigned long newsize = roundup_pow_of_two(size);
+	unsigned long newsize;
+
+	if (size > max)
+		return max;
+
+	newsize = roundup_pow_of_two(size);
 
 	if (newsize <= max / 32)
 		newsize = newsize * 4;
-- 
2.7.4

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Re: [PATCH] bug:roundup_pow_of_two(size) will return 0 when size > 2^63 because of overflow problem. fix:when size > max, return max. (when newsize > max will return max originally)

[Matthew Wilcox]

You messed up the email so that the explanation went into the subject line ...


Subject: [PATCH] bug:roundup_pow_of_two(size) will return 0     when size >
        2^63 because of overflow problem. fix:when size > max, return max.
        (when newsize > max will return max originally)

Have you observed this happening?  How did req_size become larger than 2^63?

On Fri, Oct 27, 2017 at 01:32:45PM +0000, ? ?? wrote:
> Signed-off-by: LongPing.WEI <weilongpingshu@hotmail.com>
> ---
>  mm/readahead.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/readahead.c b/mm/readahead.c
> index c4ca702..4941f04 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -248,7 +248,12 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
>   */
>  static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
>  {
> -	unsigned long newsize = roundup_pow_of_two(size);
> +	unsigned long newsize;
> +
> +	if (size > max)
> +		return max;
> +
> +	newsize = roundup_pow_of_two(size);
>  
>  	if (newsize <= max / 32)
>  		newsize = newsize * 4;
> -- 
> 2.7.4
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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