linux-kernel - Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH attached)

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Date:	Thu, 11 Sep 2008 06:53:44 -0600
From:	Joe Peterson <joe@...rush.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH
 attached)

Andrew Morton wrote:
> On Tue, 09 Sep 2008 14:42:12 -0600
> Joe Peterson <joe@...rush.com> wrote:
> 
>> 1) Fix tab erasure handling
>> 2) Improve locking when working with the echo buffer
>> 3) Remove the big kernel lock (BKL) from n_tty
>>
>> Tab erasure handling is now more robust and able to handle non-zero
>> canon column cases more correctly.  This is done by making correct use
>> of what is known in the eraser function (read buffer contents) and what
>> is known at the time of processing the tab erasure (column state).
>>
>> Also, better locking of the echo buffer will now prevent any attempts to
>> process partial multi-byte echo operations.  And since the echo buffer
>> code now isolates the tty column state code to the process_out* and
>> process_echoes functions, we can remove the big kernel lock (BKL)
>> and replace it with more modern mutex locks.
> 
> Boy.  Has this been carefully tested with lockdep enabled?

Yes, I have the following in my kernel config:

CONFIG_KALLSYMS_ALL=y
CONFIG_RT_MUTEX_TESTER=y
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
CONFIG_LOCKDEP=y
CONFIG_LOCK_STAT=y
CONFIG_DEBUG_LOCKDEP=y
CONFIG_TRACE_IRQFLAGS=y
CONFIG_STACKTRACE=y

I have run the various tests that I used to find/investigate the echo
loss problem to begin with (i.e. that make output compete with echo).
Also some manual tests that fill the echo buffer during a stopped tty,
test the eraser interaction, etc.  Things look fine so far.

						-Joe
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