linux-kernel - Re: Possible software flow problem in serial

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Message-ID: <532B90C2.8080405@hurleysoftware.com>
Date:	Thu, 20 Mar 2014 21:07:14 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Bollinger, Seth" <Seth.Bollinger@...i.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-serial <linux-serial@...r.kernel.org>
Subject: Re: Possible software flow problem in serial_core

On 03/20/2014 08:48 PM, Bollinger, Seth wrote:
>
>> Yeah, you're right; thanks for catching this.
>> (I was busy looking at the ll driver and completely missed the bug in
>> the serial core).
>>
>> uart_start() should not be conditioning the call to start_tx() on
>> the ring buffer being empty; ll drivers should already be able to handle
>> that because CTS flow control change will start_tx regardless of the ring
>> buffer count.
>>
>> Will you send a patch?
>
> Sure thing.  Just to be clear, you want to remove the ring buffer tests
> and leave the tty tests, right?

Yes. I would remove the NULL ptr test for xmit.buf as well. That way
we can uncover any bugs in the ll drivers that mistakenly depend on it.

The !stopped and !hw_stopped tests must remain.

> This will have to wait for the morning though.  :)

Take your time. TTY/serial trees are closed until 3.15-rc1 anyway.
Please be sure to address the patch to the serial maintainers.
You can cc me in the patch.

Thanks again,
Peter Hurley
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