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From: Ingo Molnar <mingo@elte.hu>
To: alfred@leakybucket.org
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2 futex questions
Date: Wed, 25 Sep 2002 10:23:16 +0200 (CEST)	[thread overview]
Message-ID: <Pine.LNX.4.44.0209251015320.4690-100000@localhost.localdomain> (raw)
In-Reply-To: <20020925003353.GA15418@closet.leakybucket.org>


On Tue, 24 Sep 2002 alfred@leakybucket.org wrote:

> 1) There's a comment in sys_futex(...) that says pos_in_page must not be
> on a page boundary. Could someone explain why?

what it wants to say: 'the futex word must not overflow into the next
page', ie. the futex word needs to be on a single page.

> 2) How is this ever true:
> 	pos_in_page + sizeof(int) > PAGE_SIZE
> when checking if pos_in_page is valid?

the full test is this:

        pos_in_page = ((unsigned long)uaddr) % PAGE_SIZE;

        if ((pos_in_page % __alignof__(int)) != 0
            || pos_in_page + sizeof(int) > PAGE_SIZE)
                return -EINVAL;

what it says: 'uaddr must be naturally aligned, and the word must be on a
single page'. In theory it's possible that __alignof__(int) !=
sizeof(int).

	Ingo


  reply	other threads:[~2002-09-25  8:09 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-09-25  0:33 alfred
2002-09-25  8:23 ` Ingo Molnar [this message]
2002-09-25  1:14   ` [patch] " alfred

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