linux-kernel - Re: [PATCH] Fix generic hugetlb pte check return type.

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Message-ID: <20301.1380790457@warthog.procyon.org.uk>
Date:	Thu, 03 Oct 2013 09:54:17 +0100
From:	David Howells <dhowells@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	dhowells@...hat.com, sparclinux@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix generic hugetlb pte check return type.

David Miller <davem@...emloft.net> wrote:

> The include/asm-generic/hugetlb.h stubs that just vector huge_pte_*()
> calls to the pte_*() implementations won't work in certain situations.
> 
> x86 and sparc, for example, return "unsigned long" from the bit
> checks, and just go "return pte_val(pte) & PTE_BIT_FOO;"
> 
> But since huge_pte_*() returns 'int', if any high bits on 64-bit are
> relevant, they get chopped off.
> 
> The net effect is that we can loop forever trying to COW a huge page,
> because the huge_pte_write() check signals false all the time.
> 
> Reported-by: Gurudas Pai <gurudas.pai@...cle.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>

Acked-by: David Howells <dhowells@...hat.com>
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