linux-kernel - Re: jsm: remove buggy write queue

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Date:	Thu, 22 Sep 2011 15:38:09 -0700
From:	Greg KH <greg@...ah.com>
To:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
Cc:	stable@...nel.org, Breno Leitao <leitao@...ux.vnet.ibm.com>,
	lucaskt@...ux.vnet.ibm.com, Alan Cox <alan@...ux.intel.com>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: jsm: remove buggy write queue

On Tue, Sep 13, 2011 at 02:55:23PM -0300, Thadeu Lima de Souza Cascardo wrote:
> jsm uses a write queue that copies from uart_core circular buffer. This
> copying however has some bugs, like not wrapping the head counter. Since
> this write queue is also a circular buffer, the consumer function is
> ready to use the uart_core circular buffer directly.
> 
> This buggy copying function was making some bytes be dropped when
> transmitting to a raw tty, doing something like this.
> 
> [root@...tname ~]$ cat /dev/ttyn1 > cascardo/dump &
> [1] 2658
> [root@...tname ~]$ cat /proc/tty/drivers > /dev/ttyn0
> [root@...tname ~]$ cat /proc/tty/drivers
> /dev/tty             /dev/tty        5       0 system:/dev/tty
> /dev/console         /dev/console    5       1 system:console
> /dev/ptmx            /dev/ptmx       5       2 system
> /dev/vc/0            /dev/vc/0       4       0 system:vtmaster
> jsm                  /dev/ttyn     250 0-31 serial
> serial               /dev/ttyS       4 64-95 serial
> hvc                  /dev/hvc      229 0-7 system
> pty_slave            /dev/pts      136 0-1048575 pty:slave
> pty_master           /dev/ptm      128 0-1048575 pty:master
> unknown              /dev/tty        4 1-63 console
> [root@...tname ~]$ cat cascardo/dump
> /dev/tty             /dev/tty        5       0 system:/dev/tty
> /dev/console         /dev/console    5       1 system:console
> /dev/ptmx            /dev/ptmx       5       2 system
> /dev/vc/0            /dev/vc/0       4       0 system:vtmaste[root@...tname ~]$
> 
> This patch drops the driver write queue entirely, using the circular
> buffer from uart_core only.
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
> ---
> 
> Hello, Greg.
> 
> This should probably go to 3.1 and stable releases, since it fixes a
> bug.

I already have this in my tree queued up for 3.2, so please remind me of
this when it hits Linus's tree during the 3.2 merge window.

thanks,

greg k-h
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