linux-kernel - Re: [PATCH] pci_get_device call from interrupt in reboot fixups

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Message-Id: <20070807004455.b634c5d0.akpm@linux-foundation.org>
Date:	Tue, 7 Aug 2007 00:44:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Greg KH <gregkh@...e.de>, "Denis V. Lunev" <den@...ru>,
	"Denis V. Lunev" <den@...nvz.org>, dev@...nvz.org,
	devel@...nvz.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci_get_device call from interrupt in reboot fixups

On Tue, 7 Aug 2007 00:24:37 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> > Andrew, I really don't want to change the PCI core to handle this, as we
> > finally fixed a lot of issues with drivers trying to walk these lists
> > from interrupt context.  So if you want to just hide the warning message
> > as we are shutting down, that's fine with me.  Or just don't do the
> > fixups.  But grabbing a reference to the pci device is unsafe in my
> > opinion and I do not want to do that.
> > 
> 
> OK, good decision ;)
> 
> One approach would be for some brave soul to pick his way through
> the reboot code and ensure that we are correctly and reliably setting
> system_state to SYSTEM_RESTART, then test that in __might_sleep().
> 
> But this does suppress somewhat-useful debugging just because of sysrq-B
> and I really wouldn't want to utilise the horrid system_state any more that
> we are presently doing.  I think on balance that it would be better if we
> could do something more targetted, like modify emergency_restart() to test
> in_interrupt() and to then apologetically set some well-named global flag
> which will shut up __might_sleep().  Pretty foul, but I can't think of
> anything better.

ok, this might be better.  How about we just stop calling mach_reboot_fixups()
at sysrq-B time?

> > >>  handle_sysrq
> > >>    machine_emergency_restart
> > >>      mach_reboot_fixups
> > >>        pci_get_device
> > >>          pci_get_subsys
> > >> 	   down_read
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