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Date: Mon, 11 Jul 2005 18:44:29 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
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To: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Cc: linux-kernel@vger.kernel.org, Andi Kleen <ak@suse.de>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: [RFC][PATCH] i386: Per node IDT
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Hello Zwane,

Zwane Mwaikambo wrote:
>
> > On Mon, 11 Jul 2005, Oleg Nesterov wrote:
> >
> > Could you explain this change? I think it breaks do_signal/handle_signal,
> > they check orig_eax >= 0 to handle -ERESTARTSYS:
> >
> > 	/* Are we from a system call? */
> > 	if (regs->orig_eax >= 0) {
> > 		/* If so, check system call restarting.. */
> > 		switch (regs->eax) {
> > 		        case -ERESTART_RESTARTBLOCK:
> > 			case -ERESTARTNOHAND:
>
> The change is so that we can send IRQs higher than 256 to do_IRQ. That 
> looks like it tries to check if we came in via system_call since we'd save 
> the system call number as orig_eax. Now that i think about it, doesn't 
> that path always get taken when we interrupt userspace and have pending 
> signals on return from interrupt?

As far as I can see, we always have orig_eax < 0 on interrupt, because

irq_entries_start:
	pushl $vector-256	<-----  orig_eax
	jmp common_interrupt

and NR_IRQS < 256. So if we have pending signals on return from interrupt,
do_signal() will not corrupt userspace registers when regs->eax == -ERESTART...
accidentally.

Probably it makes sense to change it to
	pushl $vector - 0xFFFF - 1

and in do_IRQ()
	int irq = regs->orig_eax & 0xFFFF

if you need to send IRQs higher than 256 to do_IRQ.

Oleg.