linux-kernel - Re: [RFC][PATCHv4 0/6] printk: use printk_safe to handle printk() recursive calls

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Date:   Thu, 27 Oct 2016 20:30:50 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Laura Abbott <labbott@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv4 0/6] printk: use printk_safe to handle printk()
 recursive calls

On Thu, Oct 27, 2016 at 8:49 AM, Sergey Senozhatsky
<sergey.senozhatsky@...il.com> wrote:
>
>         RFC
>
>         This patch set extends a lock-less NMI per-cpu buffers idea to
> handle recursive printk() calls. The basic mechanism is pretty much the
> same -- at the beginning of a deadlock-prone section we switch to lock-less
> printk callback, and return back to a default printk implementation at the
> end; the messages are getting flushed to a logbuf buffer from a safer
> context.

This looks very reasonable to me.

Does this also obviate the need for "printk_deferred()" that the
scheduler and the clock code uses?  Because that would be a lovely
thing to look at if it doesn't..

             LInus