linux-kernel - Re: [PATCH] serial: core: prevent softlockups on slow consoles

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 4 Sep 2015 06:42:26 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH] serial: core: prevent softlockups on slow consoles

On 09/04/2015 03:19 AM, Vitaly Kuznetsov wrote:
> Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:

>> I don't like this, please narrow this down to the real problem that your
>> hardware has here, the putchar function should not be this slow.  If it
>> is, something is wrong.
> 
> I'm afraid this is really the case:
> 
> 3)               |                                          serial8250_console_putchar() {
> 3)               |                                            wait_for_xmitr() {
> 3) # 3111.189 us |                                              io_serial_in();
> 3) # 3115.334 us |                                            }
> 3) # 2234.099 us |                                            io_serial_out();
> 3) # 5353.883 us |                                          }
> 
> This is one char and I use local pipe for Hyper-V output. In case
> something like remote pipe is in use ...
> 
> So I'm sorry, but I don't really understand the suggestion to 'narrow
> this down' - this is how slow Hyper-V serial's implementation is,
> io_serial_in() is just an inb() and io_serial_out() is an outb().

That corresponds to 330-440 baud. As far as I'm concerned, that's broken.

Regards,
Peter Hurley

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/