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

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Message-ID: <1280910830.1902.144.camel@pasglop>
Date:	Wed, 04 Aug 2010 18:33:50 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	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 00:59 -0700, Dmitry Torokhov wrote:
> Noone is using tty argument so let's get rid of it.

While talking about sysrq...

I noticed that serial drivers call sysrq with the uart lock held.

I've seen deadlocks caused by that, for example, when entering the
debugger, it waits forever for a CPU which is itself waiting on the UART
lock.

I have a patch to drop the lock in serial_core.h, I'll post that
tomorrow hopefully, just checking if there's any objection there ? The
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.

Cheers,
Ben.

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