linux-kernel - Re: RFC: do get_rtc

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Message-ID: <20070816110547.166d96e5@the-village.bc.nu>
Date:	Thu, 16 Aug 2007 11:05:47 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"David P. Reed" <dpreed@...d.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: RFC: do get_rtc_time() correctly

> I understand that SMM/SMI servicing can take a long time, but SMM/SMI 
> shouldn't  happen while interrupts are masked using local_irq_disable() 

Don't bet on it. 

> [included in spin_lock_irq()], at least on x86-architectures.  If 
> SMM/SMI can happen even then, the NMI fix below could be generalized.
> 
> My mention of NMI (which by definition can't be masked) is because NMI 

On x86 you can mask NMI briefly if you are willing to do a bit of CPU
abuse. Force an NMI, longjmp out of the handler, and NMI is off until the
next iret instruction or similar.

We don't do this and I think Linus would object to anyone who did 8)
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