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Date: Mon, 23 Jul 2001 13:15:31 -0700
Message-Id: <p05100301b78235dce19e@[10.0.0.49]>
From: "Jonathan Lundell" <jlundell@pobox.com>
To: "Linus Torvalds" <torvalds@transmeta.com>,
        "Andrea Arcangeli" <andrea@suse.de>
Cc: "Jeff Dike" <jdike@karaya.com>, user-mode-linux-user@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, "Jan Hubicka" <jh@suse.cz>
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In-Reply-To: <Pine.LNX.4.33.0107231259520.13272-100000@penguin.transmeta.com>
Subject: Re: user-mode port 0.44-2.4.7
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At 1:00 PM -0700 2001-07-23, Linus Torvalds wrote:
>On Mon, 23 Jul 2001, Andrea Arcangeli wrote:
>>
>>  gcc can assume 'state' stays constant in memory not just during the
>>  'case'.
>
>The point is that if the kernel has _any_ algorithm where it cares, it's a
>kernel bug. With volatile or without.
>
>SHOW ME THE CASE WHERE IT CARES. Let's fix it. Let's not just hide it with
>"volatile".

in arch/i386/kernel/io_apic.c:

>static int __init timer_irq_works(void)
>{
>	unsigned int t1 = jiffies;
>
>	sti();
>	/* Let ten ticks pass... */
>	mdelay((10 * 1000) / HZ);
>
>	/*
>	* Expect a few ticks at least, to be sure some possible
>	* glue logic does not lock up after one or two first
>	* ticks in a non-ExtINT mode.  Also the local APIC
>	* might have cached one ExtINT interrupt.  Finally, at
>	* least one tick may be lost due to delays.
>	*/
>	if (jiffies - t1 > 4)
>		return 1;
>
>	return 0;
>}

If jiffies were not volatile, this initializing assignment and the 
test at the end could be optimized away, leaving an unconditional 
"return 0". A lock is of no help.
-- 
/Jonathan Lundell.
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