linux-kernel - Re: [PATCH] hvc_console: fix dropping of characters when output byte channel is full

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]

Message-Id: <20100914121721.c8671ed8.akpm@linux-foundation.org>
Date:	Tue, 14 Sep 2010 12:17:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Timur Tabi <timur@...escale.com>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	benh@...nel.crashing.org, kumar.gala@...escale.com,
	amit.shah@...hat.com
Subject: Re: [PATCH] hvc_console: fix dropping of characters when output
 byte channel is full

On Fri, 20 Aug 2010 13:45:21 -0500
Timur Tabi <timur@...escale.com> wrote:

> hvc_console_print() calls the HVC client driver's put_chars() callback
> to write some characters to the console.  If the callback returns 0, that
> indicates that no characters were written (perhaps the output buffer is
> full), but hvc_console_print() treats that as an error and discards the
> rest of the buffer.
> 
> So change hvc_console_print() to just loop and call put_chars() again if it
> returns a 0 return code.

Seems rather dangerous.  The upper layer will sit there chewing 100%
CPU for as long as the lower layer is congested.

> This change makes hvc_console_print() behave more like hvc_push(), which
> does check for a 0 return code and re-schedules itself.

Yes, hvc_push() reschedules.  It doesn't sit in a tight loop burning
electrons!

Can we do something safer&smarter here?
--
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/