linux-kernel - Re: [PATCH 27/38] Rearrange buffer formatting in printk()

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Message-ID: <20140930193714.GH2707@dhcp128.suse.cz>
Date:	Tue, 30 Sep 2014 21:37:14 +0200
From:	Petr Mladek <pmladek@...e.cz>
To:	Hannes Reinecke <hare@...e.de>
Cc:	James Bottomley <jbottomley@...allels.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-scsi@...r.kernel.org, Robert Elliott <elliott@...com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 27/38] Rearrange buffer formatting in printk()

On Tue 30-09-14 18:16:20, Petr Mladek wrote:
> On Mon 29-09-14 13:58:56, Hannes Reinecke wrote:
> > Move buffer formatting to the start of the function as it
> > doesn't require to be done under any locks.
> > No functional change, required by the next patch.
> > 
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: LKML <linux-kernel@...r.kernel.org>
> 
> printk stuff is maintained by Andrew in mm tree, so adding him into CC.
> 
> > Signed-off-by: Hannes Reinecke <hare@...e.de>
> 
> Reviewed-by: Petr Mladek <pmladek@...e.cz>

I have just realized that textbuf[LOG_LINE_MAX] is a static variable.
It means that it must be used under the lock and this patch is wrong.
I want to take back the Reviewed-by and instead do

Nacked->by: Petr Mladek <pmladek@...e.cz>

also it means that it does not take the extra space on the stack
and you probably does not need the two patches at all.

Best Regards,
Petr
 
> I do not see any obvious problem. Just note that
> [sched_delayed] has already been removed in -mm tree. You might
> want to base this patch on top of the commit 460d73c35ffa17979422290
> ("printk: git rid of [sched_delayed] message for printk_deferred")
> from linux-next.
> 
> Best Regards,
> Petr
> 
> > ---
> >  kernel/printk/printk.c | 21 ++++++++++-----------
> >  1 file changed, 10 insertions(+), 11 deletions(-)
> > 
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 1ce7706..d13675e 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -1633,8 +1633,18 @@ asmlinkage int vprintk_emit(int facility, int level,
> >  	if (level == SCHED_MESSAGE_LOGLEVEL) {
> >  		level = -1;
> >  		in_sched = true;
> > +
> > +		/*
> > +		 * The printf needs to come first; we need the syslog
> > +		 * prefix which might be passed-in as a parameter.
> > +		 */
> > +		text_len = scnprintf(text, sizeof(textbuf),
> > +				     KERN_WARNING "[sched_delayed] ");
> >  	}
> >  
> > +	text_len += vscnprintf(text + text_len,
> > +			       sizeof(textbuf) - text_len, fmt, args);
> > +
> >  	boot_delay_msec(level);
> >  	printk_delay();
> >  
> > @@ -1676,17 +1686,6 @@ asmlinkage int vprintk_emit(int facility, int level,
> >  					 strlen(recursion_msg));
> >  	}
> >  
> > -	/*
> > -	 * The printf needs to come first; we need the syslog
> > -	 * prefix which might be passed-in as a parameter.
> > -	 */
> > -	if (in_sched)
> > -		text_len = scnprintf(text, sizeof(textbuf),
> > -				     KERN_WARNING "[sched_delayed] ");
> > -
> > -	text_len += vscnprintf(text + text_len,
> > -			       sizeof(textbuf) - text_len, fmt, args);
> > -
> >  	/* mark and strip a trailing newline */
> >  	if (text_len && text[text_len-1] == '\n') {
> >  		text_len--;
> > -- 
> > 1.8.5.2
> > 
> > --
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