linux-kernel - Re: [PATCH] printk: introduce should_ignore

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Message-ID: <20160627130430.GA566@swordfish>
Date:	Mon, 27 Jun 2016 22:04:30 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Jan Kara <jack@...e.cz>,
	Calvin Owens <calvinowens@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: introduce should_ignore_loglevel()

On (06/27/16 11:26), Petr Mladek wrote:
> On Sat 2016-06-25 14:22:37, Sergey Senozhatsky wrote:
> > On (06/24/16 18:05), Petr Mladek wrote:
> > [..]
> > > > +static bool should_ignore_loglevel(int level)
> > > > +{
> > > > +	return (level >= console_loglevel && !ignore_loglevel);
> > > 
> > > The patch looks fine. It is nice optimization.
> > > 
> > > I was just quite confused by the name of this function. A function
> > > called should_ignore_loglevel() should not return false when
> > > ignore_loglevel variable is true.
> > > 
> > > I would call it ignore_message() or ignore_message_on_console() or so.
> > 
> > Hello Petr, you are right.
> > 
> > I was thinking about
> > 
> > s/should_ignore_loglevel/suppress_message/g
> > or.... s/should_ignore_loglevel/suppress_message_by_level/g
> > s/should_ignore_loglevel/suppress_message_printing/g
> > 
> > suppress_message_printing() is probably fine.
> 
> All variants look fine to me. After renaming, feel free to
> add:
> 
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> 

thanks.

> PS: The ignore_loglevel handling is a bit racy in some situations.
> For example, uv_nmi_dump_state() or __handle_sysrq() set another
> level, print some messages, and restore the original level. They
> do not wait until all the printed messages appear on the console.
> Also they do not synchronize against each other.
>

__handle_sysrq() also assumes that only cpu printk-s, so it does
KERN_CONT printks in SMP mode. and there are billions of places
that do things like this.

as of deferred loglevel check, we probably can add "console_loglevel:3;"
to 'struct printk_log' and `static struct cont', and keep there
console_loglevel actual at the time the was appeneded to the log
buffer. so then suppress_message_printing() will have one extra param

bool suppress_message_printing(int leve, int cons_loglevel)
{
	return (level >= cons_loglevel ...);
}


speaking of KERN_CONT, I've found one regression with async printk,
and I think I now have some idea what's going on there, will post
some-sort-of-a-patch today or tomorrow.


> I am not sure if we have already discussed this. It is not critical
> and it works well most of the time. I just want to make sure that
> you know about it as you have more plans with the printk/console code.

thanks, I'll put in on a list; not sure we discussed this either.

	-ss