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Date:   Thu, 1 Dec 2016 11:14:07 +0900
From:   Sergey Senozhatsky <>
To:     Petr Mladek <>
Cc:     Sergey Senozhatsky <>,
        Andrew Morton <>,
        Jan Kara <>, Tejun Heo <>,
        Calvin Owens <>,
        Thomas Gleixner <>,
        Mel Gorman <>,
        Steven Rostedt <>,
        Ingo Molnar <>,
        Peter Zijlstra <>,
        Laura Abbott <>,
        Andy Lutomirski <>,
        Linus Torvalds <>,
        Kees Cook <>,,
        Sergey Senozhatsky <>
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.


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