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

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Message-ID: <55BAB8F4.1060205@hurleysoftware.com>
Date:	Thu, 30 Jul 2015 19:53:24 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	John Ogness <john.ogness@...utronix.de>
CC:	linux-kernel@...r.kernel.org,
	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 07:15 PM, Peter Hurley wrote:
> 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.

Also, seriously consider if you want to use that TI line discipline at all.

If you're using it only for bluetooth w/ kernel bluetooth stack, you don't
need btwilink + st_drv anyway.

Regards,
Peter Hurley
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