linux-kernel - Re: [PATCH 1/1] TTY: tty

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Date:	Tue, 26 Nov 2013 20:13:36 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Jiri Slaby <jslaby@...e.cz>, gregkh@...uxfoundation.org
CC:	jirislaby@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] TTY: tty_buffer, warn on leaks

On 11/11/2013 06:13 PM, Peter Hurley wrote:
> On 11/11/2013 03:05 PM, Jiri Slaby wrote:
>> When we leak something, warn about that. For that we need to account
>> the memory used also in the free_all method. It is handled elsewhere
>> correctly.
>
> Hi Jiri,
>
> Good idea.
>
>> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
>> ---
>>   drivers/tty/tty_buffer.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
>> index 5f08c39e76ab..20cb9492dbf8 100644
>> --- a/drivers/tty/tty_buffer.c
>> +++ b/drivers/tty/tty_buffer.c
>> @@ -115,21 +115,27 @@ void tty_buffer_free_all(struct tty_port *port)
>>       struct tty_bufhead *buf = &port->buf;
>>       struct tty_buffer *p, *next;
>>       struct llist_node *llist;
>> +    int zero = 0;
>>
>>       while ((p = buf->head) != NULL) {
>>           buf->head = p->next;
>> +        atomic_sub(p->size, &buf->memory_used);
>
> buf->memory_used doesn't need to be treated atomically here,
> and doing so implies that it's necessary.
>
> Accumulating p->size in a non-atomic local is probably better.
>
>>           if (p->size > 0)
>>               kfree(p);
>>       }
>>       llist = llist_del_all(&buf->free);
>> -    llist_for_each_entry_safe(p, next, llist, free)
>> +    llist_for_each_entry_safe(p, next, llist, free) {
>> +        atomic_sub(p->size, &buf->memory_used);
>
> Same here.

Sorry, I forgot:  the buffers on the free list have already been
accounted for in tty_buffer_free() so don't form part of the
buf->mem_used total.

The buffer memory accounting was like that in 3.7 so I left it in.

static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
{
	struct tty_bufhead *buf = &port->buf;

	/* Dumb strategy for now - should keep some stats */
	WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);

	if (b->size > MIN_TTYB_SIZE)
		kfree(b);
	else if (b->size > 0)
		llist_add(&b->free, &buf->free);
}

Regards,
Peter Hurley

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