linux-kernel - Re: [PATCHv7 6/8] printk: use printk

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Date:   Thu, 2 Feb 2017 10:07:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>, Jan Kara <jack@...e.cz>,
        Ross Zwisler <zwisler@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Calvin Owens <calvinowens@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv7 6/8] printk: use printk_safe buffers in printk

On Thu, Feb 02, 2017 at 11:11:34AM +0900, Sergey Senozhatsky wrote:
> On (02/01/17 16:39), Petr Mladek wrote:
> [..]
> > I guess that you are talking about the introduction of
> > #define SCHED_WARN_ON(x)	WARN_ONCE(x, #x)
> 
> my guess would be that Jan was talking about printk_deferred() patch.
> it's on my TODO list.
> 
> I want to entirely remove console_sem and scheduler out of printk() path.
> that's the only way to make printk() deadlock safe.

And useless.. if you never get around to the 'later' part where you
print the content. This way you still mostly get the output.

And no, its not the only way, see my printk->early_printk patches. early
serial console only does a loop over outb, impossible to mess that up.