linux-kernel - Re: printk() vs tty

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Message-ID: <CA+55aFwu+oSPtqfN+bS3_fHXWU+VMd5BGhNd=J4MjuAJZT+fTQ@mail.gmail.com>
Date:	Wed, 14 Dec 2011 07:54:47 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Ted Ts'o" <tytso@....edu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg KH <greg@...ah.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: printk() vs tty_io

On Wed, Dec 14, 2011 at 6:23 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> printk() goes through serial8250_console_write() which writes to the
>> UART device using a busy loop, with local IRQ's disabled.  So it's not
>> serial8250_console_write() which is waking things up; this is coming
>> form interrupt handler running on some different CPU.
>
> Which can still deadlock you just fine..

Ugh. There is a *ton* of stuff inside that serial port lock,
including, yes, the uart_write_wakeup().

And it does look like it's protecting port->tty or something, so I
don't see that we can just move the wakeup to outside the lock, which
was my first reaction.

Ugh.

                  Linus
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