linux-kernel - Re: WARNING at tty_buffer.c:428 process_one

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Message-ID: <5135D072.8070101@suse.cz>
Date:	Tue, 05 Mar 2013 12:01:06 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	David Miller <davem@...emloft.net>, gregkh@...uxfoundation.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: WARNING at tty_buffer.c:428 process_one_work()

On 03/01/2013 11:00 PM, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Fri, 01 Mar 2013 16:47:11 -0500 (EST)
> 
>>
>> I'm getting these non-stop right when the hypervisor console registers
>> on sparc64, and the machine won't boot up properly.  This is with
>> Linus's current tree.
> 
> As a quick addendum I'm looking at all of these tty_insert_flip_char()
> conversions and I'm extremely disappointed.
> 
> Let's just look at just two of the sparc drivers converted in commit
> 92a19f9cec9a80ad93c06e115822deb729e2c6ad, namely sunhv.c and sunsab.c.
> 
> The changes to the uart_handle_sysrq_char() call sites are handled
> completely differently in these two drivers, in nearly identical
> situations.  How can this be correct?
> 
> In the sunhv.c case the uart_handle_sysrq_char() call is preserved
> but the guarding test is changed from:
> 
> 	if (tty == NULL)
> 
> into
> 
> 	if (port->start == NULL)
> 
> Whereas in the sunsab.c case, the entire guarding test as well as
> the uart_handle_sysrq_char() invocation itself are both
> completly removed.
> 
> How in the world can that be right?
> 
> Either the receive_chars() method's invocations of
> uart_handle_sysrq_char() should be retained, or this sysrq processing
> is handled now elsewhere and in which case that should be documented
> clearly and in detail in the commit log message.

Ok, uart_handle_sysrq_char is still there, in both of them. But since we
do not care about the tty pointer in those routines any more, the tty ==
NULL test is removed along with its body. I didn't considered that so
critical to document that in the commit log. I thought it's obvious.

All those "if (port->state == NULL)"'s are mostly wrong. Look for
example to subsab's receive_chars and transmit_chars. One checks that,
one dereferences that immediately OTOH. Yes, serial_core should ensure
the interrupts are off by the time port->state is NULL (by calling
driver's ->shutdown). I will remove the test from receive_chars too
which will make the code cleaner.

I left that "if (port->start == NULL)" in sunhv in place because it
behaves completely differently. It checks port->start on all paths prior
dereferencing it. And it does not stop interrupts on ->shutdown.

thanks,
-- 
js
suse labs
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