From: Oliver Neukum <oneukum@suse.com>
To: Johan Hovold <johan@kernel.org>, Oliver Neukum <oneukum@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] USB: cdc-acm: fix racy TIOCMIWAIT implementation
Date: Mon, 7 Sep 2026 12:28:46 +0200 [thread overview]
Message-ID: <bc055887-3029-4740-bec5-7e2fe4205992@suse.com> (raw)
In-Reply-To: <ap6LcHWDvIWF3oNK@hovoldconsulting.com>
On 07.09.26 12:01, Johan Hovold wrote:
> On Mon, Sep 07, 2026 at 11:50:41AM +0200, Oliver Neukum wrote:
>> On 07.09.26 10:47, Johan Hovold wrote:
>>> On Mon, Sep 07, 2026 at 10:17:38AM +0200, Oliver Neukum wrote:
>>>> On 07.09.26 08:55, Johan Hovold wrote:
[..]
>>> Looking at the implementation again now, it seems further changes are
>>> needed to fix the implementation, though. The completion handler should
>>> not be updating old_count. That's for each TIOCMIWAIT to do.
>>
>> I am sorry to be obnoxious about that, but I am afraid that would
>> break TIOCGICOUNT
>
> Why do you think so? TIOCGICOUNT just returns the current counters.
Yes, but user space can call TIOCGICOUNT multiple times in sequence
_without_ calling TIOCMIWAIT in between.
In that case the counters have to increase if a line changes, don't they?
For that to happen you need to handle a status change in the completion
handler.
Regards
Oliver
next prev parent reply other threads:[~2026-09-07 10:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-07 6:55 [PATCH] USB: cdc-acm: fix racy TIOCMIWAIT implementation Johan Hovold
2026-09-07 8:17 ` Oliver Neukum
2026-09-07 8:47 ` Johan Hovold
2026-09-07 9:13 ` Johan Hovold
2026-09-07 9:50 ` Oliver Neukum
2026-09-07 10:01 ` Johan Hovold
2026-09-07 10:28 ` Oliver Neukum [this message]
2026-09-07 11:38 ` Johan Hovold
2026-09-07 12:46 ` Oliver Neukum
2026-09-07 13:03 ` Johan Hovold
2026-09-08 6:54 ` Oliver Neukum
2026-09-08 7:12 ` Johan Hovold
2026-09-08 9:23 ` Oliver Neukum
2026-09-11 6:57 ` Johan Hovold
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