linux-kernel - Re: [PATCH RESEND] sh: sq: Use the bitmap API when applicable

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Date:   Tue, 18 Apr 2023 20:05:54 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH RESEND] sh: sq: Use the bitmap API when applicable

Le 18/04/2023 à 09:14, Geert Uytterhoeven a écrit :
> 
> Nice catch!
> 
> Looking more deeply at the code, the intention is to allocate a bitmap
> with nr_pages bits, so the code fater Christophe's patch is correct.
> However, the old code is indeed wrong:
> 
>      (nr_pages + (BITS_PER_LONG - 1)) / BITS_PER_LONG
> 
> The aim is to calculate the size in bytes, rounded up to an integral
> number of longs, but it lacks a final multiplication by BITS_PER_BYTE,
> so it's off by a factor of 4.
> 
> Fixes: d7c30c682a278abe ("sh: Store Queue API rework.")
> 
> As we didn't have bitmap_zalloc() until commit c42b65e363ce97a8
> ("bitmap: Add bitmap_alloc(), bitmap_zalloc() and bitmap_free()")
> in v4.19, it would be good to fix the bug first in a separate patch,
> not using
> 
> BTW, interesting how this got missed when fixing the other out-of-range
> bug in commit 9f650cf2b811cfb6 ("sh: Fix store queue bitmap end.",
> s/marc.theaimsgroup.com/marc.info/ when following the link).

So, this means that this got unnoticed for 16 years?
Waouh!

I would never have thought that a "trivial" clean-up that I took time to 
repost could trigger such a thing!

Again.
Waouh!


Maybe, 0x04000000 is way to big?
Anyone knows where this value comes from?

Could there have been some memory corruption in real world application?

CJ

> 
> Gr{oetje,eeting}s,
> 
>                          Geert
>