linux-kernel - Re: [PATCH] powerpc/64e: Fix wrong test in __ptep_test_and_clear

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Message-ID: <87a5u1ibwr.fsf@mail.lhotse>
Date:   Tue, 05 Sep 2023 12:36:36 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/64e: Fix wrong test in
 __ptep_test_and_clear_young()

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> Commit 45201c879469 ("powerpc/nohash: Remove hash related code from
> nohash headers.") replaced:
>
>   if ((pte_val(*ptep) & (_PAGE_ACCESSED | _PAGE_HASHPTE)) == 0)
> 	return 0;
>
> By:
>
>   if (pte_young(*ptep))
> 	return 0;
>
> But it should be:
>
>   if (!pte_young(*ptep))
> 	return 0;


That seems bad :)

But I don't know off the top of my head where
__ptep_test_and_clear_young() is used, and so what the symptoms could
be. Presumably nothing too bad or someone would have noticed?

cheers