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Date:   Tue, 29 Dec 2020 10:11:11 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Toralf Förster <toralf.foerster@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH 2/2] mm: readahead: handle LARGE input to
 get_init_ra_size()

On 12/29/20 10:01 AM, Toralf Förster wrote:
> On 12/23/20 2:50 AM, Randy Dunlap wrote:
>>> What motivates this change?  Is there any reason to think this can
>>> happen?
>> Spotted in the wild:
> I run 2 hardened Gentoo systems, a server and a desktop.
> 
> I patched the server with this:
> 
> mr-fox ~ # cat ubsan.patch
> --- linux-5.10.1.orig/mm/readahead.c
> +++ linux-5.10.1/mm/readahead.c
> @@ -310,7 +310,11 @@ void force_page_cache_ra(struct readahea
>   */
>  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)
> +               size = 32;
> +       newsize = roundup_pow_of_two(size);
> 
>         if (newsize <= max / 32)
>                 newsize = newsize * 4;
> 
> 
> 
> and the issue did no longer occurred at the server (5.10.2).
> 
> I did not patched the desktop system and the issue occurred still 3
> times since 21th of december (5.10.2/3)

Yes, that's the patch that I posted on 2020-DEC-22.

Looks like I should submit a real patch for that.

thanks.
-- 
~Randy

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