linux-kernel - Re: [PATCH] tty: serial: msm: Fix lock init issue with earlycon

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Message-ID: <5446B708.6070404@hurleysoftware.com>
Date:	Tue, 21 Oct 2014 15:42:00 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Kumar Gala <galak@...eaurora.org>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH] tty: serial: msm: Fix lock init issue with earlycon

On 10/20/2014 06:20 PM, Stephen Boyd wrote:
> On 10/20, Stephen Boyd wrote:
>> On 10/20, Peter Hurley wrote:
>>>
>>> FWIW, __msm_console_write() is a deadlock-waiting-to_happen since it does
>>> not disable interrupts with spin_lock_irqsave().
>>>
>>
>> Yeah we should fix that. As far as I can tell we've never used
>> the irqsave variant of the lock in the console path. Did this
>> become necessary at some point since this driver was introduced?
>> I'm wondering how many stable trees need the fix.
> 
> Actually I don't see this case. It looks like the console is
> always called in call_console_drivers() with irqs saved and
> disabled via the logbuf_lock in console_cont_flush() or
> console_unlock().

Thanks for bringing that to my attention.

That looks like a vestige of the initial transition away from BKL.
I might look into just disabling preemption; even that might not
really be necessary.

Regards,
Peter Hurley

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