linux-kernel - Re: [PATCH v2] n_tty: Fix read_buf race condition, increment read

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Message-ID: <CABkLObqGP2488XYCATKE_U-uDjo=tWgEAaU2+YkwstDTnoeetA@mail.gmail.com>
Date:	Wed, 12 Nov 2014 08:28:56 +0100
From:	Christian Riesch <christian.riesch@...cron.at>
To:	Måns Rullgård <mans@...sr.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] n_tty: Fix read_buf race condition, increment
 read_head after pushing data

On Tue, Nov 11, 2014 at 2:04 PM, Måns Rullgård <mans@...sr.com> wrote:
> Christian Riesch <christian.riesch@...cron.at> writes:
[...]>> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
>> index 2e900a9..b09f326 100644
>> --- a/drivers/tty/n_tty.c
>> +++ b/drivers/tty/n_tty.c
>> @@ -321,7 +321,9 @@ static void n_tty_check_unthrottle(struct tty_struct *tty)
>>
>>  static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
>>  {
>> -     *read_buf_addr(ldata, ldata->read_head++) = c;
>> +     *read_buf_addr(ldata, ldata->read_head) = c;
>> +     /* increment read_head _after_ placing the character in the buffer */
>> +     ldata->read_head++;
>>  }
>
> Is that comment really necessary?

No, I am pretty sure that removing the comment would not break the code ;-)

I just thought it would be good to have some kind of reminder here.
Otherwise someone may think: Hey, it would be a good idea to do the
increment right in the first line. And submit a patch for it.
But I am also ok with removing the comment. So if you like me to post
a v3 without the comment, I'll be happy to do that.

Christian
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