linux-kernel - Re: [PATCH] tty: Correct tty buffer flushing.

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Date:	Thu, 29 Nov 2012 18:03:49 +0400
From:	Ilya Zykov <ilya@...x.ru>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Xiaobing Tu <xiaobing.tu@...el.com>,
	Alan Cox <alan@...ux.intel.com>, Jiri Slaby <jslaby@...e.cz>,
	Alek Du <alek.du@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] tty: Correct tty buffer flushing.

On 29.11.2012 17:54, Alan Cox wrote:
>> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
>> index 6c9b7cd..4f02f9c 100644
>> --- a/drivers/tty/tty_buffer.c
>> +++ b/drivers/tty/tty_buffer.c
>> @@ -114,11 +114,14 @@ static void __tty_buffer_flush(struct tty_struct *tty)
>>  {
>>  	struct tty_buffer *thead;
>>  
>> -	while ((thead = tty->buf.head) != NULL) {
>> -		tty->buf.head = thead->next;
>> -		tty_buffer_free(tty, thead);
>> +	if (tty->buf.head == NULL)
>> +		return;
>> +	while ((thead = tty->buf.head->next) != NULL) {
>> +		tty_buffer_free(tty, tty->buf.head);
>> +		tty->buf.head = thead;
> 
> This part of the change seems to have no effect at all. There are no
> locks held so there is nothing guaranteeing how the other processors
> views of the order of operations will be affected.
> 
> Alan
> 
/**
 *	__tty_buffer_flush		-	flush full tty buffers
 *	@tty: tty to flush
 *
 *	flush all the buffers containing receive data. Caller must
 *	hold the buffer lock and must have ensured no parallel flush to
 *	ldisc is running.
 *
 *	Locking: Caller must hold tty->buf.lock
 */

Please, don't ignore my patch.
Please, Look at it one more time thoroughly.
Before REVERT [PATCH] tty: hold lock across tty buffer finding and buffer filling.
Thank you.


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