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Date: Mon, 10 Oct 2016 13:02:49 +0200
From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Calvin Owens <calvinowens@fb.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCHv2 6/7] printk: report printk recursion from
 alt_printk flush
Message-ID: <20161010110249.GH23809@pathway.suse.cz>
References: <20160930151758.8965-1-sergey.senozhatsky@gmail.com>
 <20160930151758.8965-7-sergey.senozhatsky@gmail.com>
 <20161006154112.GJ13369@pathway.suse.cz>
 <20161007185920.GC486@swordfish>
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On Sat 2016-10-08 03:59:20, Sergey Senozhatsky wrote:
> On (10/06/16 17:41), Petr Mladek wrote:
> [..]
> > > +	if (this_cpu_read(alt_printk_ctx) & ALT_PRINTK_RECURSION_MASK) {
> > > +		const char *msg = "BUG: recent printk recursion!\n";
> > > +
> > > +		this_cpu_and(alt_printk_ctx, ~ALT_PRINTK_RECURSION_MASK);
> > > +		alt_printk_flush_line(msg, strlen(msg));
> > > +	}
> > > +
> > >  	/*
> > >  	 * This is just a paranoid check that nobody has manipulated
> > >  	 * the buffer an unexpected way. If we printed something then
> > > @@ -290,6 +297,8 @@ static int vprintk_alt(const char *fmt, va_list args)
> > >  {
> > >  	struct alt_printk_seq_buf *s = this_cpu_ptr(&alt_print_seq);
> > >  
> > > +	/* There is only one way to get here -- a printk recursion. */
> > > +	this_cpu_or(alt_printk_ctx, ALT_PRINTK_RECURSION_MASK);
> > 
> > Is it really a bug? In most cases, the message that is being printed
> > describes a bug. We just allow to print it this alternative way to
> > avoid a possible deadlock. IMHO, this might cause a confusion.
> 
> just wanted to preserve the existing behavior, but can drop it.

I see. Well, the current code drops the original message if there is a
recursion and there is no oops_in_progress. Therefore the warning
is the only way to know that a message was lost. But we store
the original message in the alternative buffer now. Therefore
it is not longer lost.

Best Regards,
Petr