linux-kernel - Re: [PATCH] tty: use printk_safe context at tty

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Date:   Tue, 6 Apr 2021 15:42:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Jiri Slaby <jirislaby@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: use printk_safe context at tty_msg()

On Tue, Apr 06, 2021 at 08:16:43PM +0900, Tetsuo Handa wrote:
> On 2021/04/06 16:10, Greg Kroah-Hartman wrote:
> > On Tue, Apr 06, 2021 at 02:31:43PM +0900, Tetsuo Handa wrote:
> >> On 2021/04/06 13:51, Jiri Slaby wrote:
> >>> On 03. 04. 21, 6:14, Tetsuo Handa wrote:
> >>>> --- a/include/linux/tty.h
> >>>> +++ b/include/linux/tty.h
> >>>> @@ -14,6 +14,7 @@
> >>>>   #include <uapi/linux/tty.h>
> >>>>   #include <linux/rwsem.h>
> >>>>   #include <linux/llist.h>
> >>>> +#include <../../kernel/printk/internal.h>
> >>>
> >>> Including printk's internal header in linux/tty.h doesn't look correct to me.
> >>>
> >>
> >> This is because this patch wants __printk_safe_enter()/__printk_safe_exit()
> >> without #ifdef'ing CONFIG_PRINTK.
> > 
> > Then those functions need to be "properly" exported, not placed only in
> > an "internal.h" file that obviously should not be included from anywhere
> > like this.
> > 
> >> Peter and Sergey, what should we do?
> >> Can we move printk_safe_enter_irqsave()/printk_safe_exit_irqrestore() to include/linux/printk.h ?
> > 
> > Are you sure that is the only way to resolve this?
> 
> Publishing printk_safe_enter_irqsave() etc. was once proposed at
> https://lkml.kernel.org/r/20181016050428.17966-3-sergey.senozhatsky@gmail.com and
> Peter Zijlstra did not like such change. But we reconfirmed that "tty_port lock must
> switch to printk_safe" at https://lkml.kernel.org/r/20190219013254.GA20023@jagdpanzerIV .
> 
> Two years has elapsed since a completely new printk implementation which would not
> use printk_safe context was proposed, but printk_safe context is still remaining.
> Therefore, we might need to tolerate, with a warning that printk_safe_enter_irqsave()
> etc. are not intended for general use, use of printk_safe context for tty_msg() and
> tty_buffer_alloc().

The printk work is still ongoing, perhaps work with those developers on
this?

thanks,

greg k-h