linux-kernel - Re: [RFC PATCH v1 08/25] printk: add ring buffer and kthread

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: <20190308100449.dccctqo6i4xa6bhq@pathway.suse.cz>
Date:   Fri, 8 Mar 2019 11:04:49 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wang <wonderfly@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Feiner <pfeiner@...gle.com>,
        linux-serial@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v1 08/25] printk: add ring buffer and kthread

On Fri 2019-03-08 10:31:34, Sergey Senozhatsky wrote:
> On (03/07/19 13:06), John Ogness wrote:
> > On 2019-03-04, Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:
> > > This, theoretically, creates a whole new world of possibilities for
> > > console drivers. Now they can do GFP_KERNEL allocations and stall
> > > printk_kthread during OOM; or they can explicitly reschedule from
> > > ->write() callback (via console_conditional_schedule()) because
> > > console_lock() sets console_may_schedule.
> > 
> This can stall the entire printing pipeline
> 
> OOM -> printk_kthread() -> console_lock() -> con_foo() -> kmalloc(GFP_KERNEL) -> OOM
> 
> > Although, as I mentioned in a previous response[0], perhaps we should
> > not loosen the requirements on write().
> 
> Right. Console drivers better stay restricted; very restricted.

I agree here.

> > It is exactly that disable_preempt() that is so harmful for realtime tasks.

> I'll reply in another email (later today, or tomorrow).

I see. But I have troubles to imagine a preemtible direct console
output. The result would be mixed messages on a single line.

Best Regards,
Petr