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Date: Thu, 1 Dec 2016 11:14:07 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        Tejun Heo <tj@kernel.org>, Calvin Owens <calvinowens@fb.com>,
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        Mel Gorman <mgorman@techsingularity.net>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Laura Abbott <labbott@redhat.com>, Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC][PATCHv4 5/6] printk: use printk_safe buffers
Message-ID: <20161201021407.GF12039@jagdpanzerIV>
References: <20161027154933.1211-1-sergey.senozhatsky@gmail.com>
 <20161027154933.1211-6-sergey.senozhatsky@gmail.com>
 <20161125142855.GI24103@pathway.suse.cz>
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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