linux-kernel - Re: [PATCH 1/3] Input: sysrq - drop tty argument from sysrq ops handlers

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Date:	Thu, 05 Aug 2010 11:59:24 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Airlie <airlied@...ux.ie>,
	David Miller <davem@...emloft.net>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jason Wessel <jason.wessel@...driver.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Russell King <linux@....linux.org.uk>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 1/3] Input: sysrq - drop tty argument from sysrq ops
 handlers

On Wed, 2010-08-04 at 10:09 +0100, Alan Cox wrote:
> 
> Fundamentally - no. However the impact it has on a lot of the drivers
> will be significant and you'll be submitting a huge patch pile to fix up
> all the locking assumptions (for one it means port->tty might change
> across any call that ends up in sysrq)

Right. That's nasty. I think we need somewhat to break the loop when
that happens as if we were getting a new interrupt to some extent.

And that's a lot of drivers to fix.

> > serial drivers might need to be audited a bit to make sure they cope
> > with the lock being dropped and re-acquired around the sysrq call.
> 
> Architecturally I think it would make more sense to add a new sysrq
> helper which merely sets a flag, and check that flag at the end of the IRQ
> when dropping the lock anyway.

Interesting idea. That does mean that multiple sysrq in one interrupt
will be coalesced but I don't see that as an issue.

> Otherwise it'll be a huge amount of work to even build test all those
> consoles.

Right. Better to have a way where we can fix them one at a time. I'll
look into it. Thanks.

Cheers,
Ben.


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