linux-kernel - Re: [PATCH 1/3] serial: 8250: unlock port for uart_write

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Message-ID: <55BAB00B.3010806@hurleysoftware.com>
Date:	Thu, 30 Jul 2015 19:15:23 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	John Ogness <john.ogness@...utronix.de>,
	linux-kernel@...r.kernel.org
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tony Lindgren <tony@...mide.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-omap@...r.kernel.org, nsekhar@...com, nm@...com,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH 1/3] serial: 8250: unlock port for uart_write_wakeup()

On 07/30/2015 06:54 PM, John Ogness wrote:
> uart_write_wakeup() should be called without holding the port lock.
> Otherwise a possible recursive spinlock issue can occur, such as
> the following callchain:
> 
> 8250_core.c:serial8250_tx_chars() - called with port locked
>  serial_core.c:uart_write_wakeup()
>   tty_io.c:tty_wakeup()
>    st_core.c:st_tty_wakeup()
>     st_core.c:st_tx_wakeup()
>      st_core.c:st_int_write()
>       serial_core.c:uart_write() - locks port

NAK.

This is a bug in the N_TI_WL line discipline, specifically in the
st_tx_wakeup() function, which cannot perform the write synchronously.

This is a common line discipline bug, and typically fixed by performing
the wakeup operations from a kworker instead.

Regards,
Peter Hurley
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