linux-kernel - Re: [RFC][PATCHv2 6/7] printk: report printk recursion from alt

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Date:   Sat, 8 Oct 2016 03:59:20 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Calvin Owens <calvinowens@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv2 6/7] printk: report printk recursion from
 alt_printk flush

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.

> Instead I would print an error when we missed some messages
> because the alternative buffer was not big enough.

ok, will do.

	-ss