linux-kernel - Re: [RFC][PATCHv4 5/6] printk: use printk

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Message-ID: <20161201021407.GF12039@jagdpanzerIV>
Date:   Thu, 1 Dec 2016 11:14:07 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.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>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv4 5/6] printk: use printk_safe buffers

On (11/25/16 15:28), Petr Mladek wrote:
[..]
> I really like this patch. The only small problem is that it enables
> lockdep and it does not explain why it is safe. The change itself
> looks fine but it took me some time to prove why. IMHO, it is
> worth a comment.
> 
> One thing is printk() recursion caused by lockdep warning
> triggered from inside vprintk_emit(). It is safe because
> the critical sections are guarded by printk_safe_enter()/exit()
> now.
> 
> Another thing is lockdep recursion caused by catching another lockdep
> issue when printing warning about the first one. This is safe
> because lockdep protects itself. First, it sets and checks
> current->lockdep_recursion around the critical sections.
> Second, further checks are disabled entirely once first
> lockdep issue is found.
> 
> If you add some comments about lockdep, feel free to use:

ok, I'll try to.

	-ss