linux-kernel - Re: [RFC PATCH 2/2] mm: readahead: handle LARGE input to get_init_ra

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Date:   Tue, 29 Dec 2020 19:01:55 +0100
From:   Toralf Förster <toralf.foerster@....de>
To:     Randy Dunlap <rdunlap@...radead.org>,
        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 12/23/20 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)

--
Toralf