linux-kernel - Re: [RFC][PATCHv4 3/6] printk: introduce per-cpu safe

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Message-ID: <20161201053247.GA7814@jagdpanzerIV>
Date:   Thu, 1 Dec 2016 14:32:47 +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 3/6] printk: introduce per-cpu safe_print seq
 buffer

On (11/24/16 17:58), Petr Mladek wrote:
[..]
> > +/*
> > + * Lockless printk(), to avoid deadlocks should the printk() recurse
> > + * into itself. It uses a per-CPU buffer to store the message, just like
> > + * NMI.
> > + */
> > +static int vprintk_safe(const char *fmt, va_list args)
> > +{
> > +	struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
> > +
> > +	return printk_safe_log_store(s, fmt, args);
> 
> We should return zero if printk_safe_log_store() returns an error.
> I know that it will get fixed in the next patch. But we should do
> some minimum sanity check here because of bisection.

by the way. vprintk_safe() and the entire printk_safe mechanism are
not yet used in this patch. the patch that enables it comes in later.

	-ss