Re: [PATCH 4.19 regression fix] printk: For early boot messages check loglevel when flushing the buffer

[Petr Mladek]

On Wed 2018-09-05 17:33:26, Sergey Senozhatsky wrote:
> On (09/05/18 14:36), Sergey Senozhatsky wrote:
> > 
> > Just a demonstration of the idea. It does not look very good, tho.
> > I'd rather have just one suppress_message_printing() in printk code.
> > 
> > // This is not a proposed patch, hence the 80-cols violation.
> > 
> > ---
> > 
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index c036f128cdc3..231ac18423e1 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -2416,7 +2416,7 @@ void console_unlock(void)
> >  			break;
> >  
> >  		msg = log_from_idx(console_idx);
> > -		if (msg->flags & LOG_NOCONS) {
> > +		if (msg->flags & LOG_NOCONS || (exclusive_console && suppress_message_printing(msg->level))) {
> >  			/*
> >  			 * Skip record if !ignore_loglevel, and
> >  			 * record has level above the console loglevel.
> 
> D'oh... Sorry about that, but, believe it or not, this is completely
> not what I had in my mind. What I had, was something like this:
> 
> ---
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index c036f128cdc3..dadb8c11b0d6 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2416,6 +2416,11 @@ void console_unlock(void)
>  			break;
>  
>  		msg = log_from_idx(console_idx);
> +
> +		if (exclusive_console &&
> +				!suppress_message_printing(msg->level))
> +			msg->flags &= ~LOG_NOCONS;

Hmm, this does not help with consoles without CON_PRINTBUFFER
flag. Note that the first registered console prints all messages
even without this flag.

Also there is "debug" earlyparam where we need the opposite. I mean
that we want to show messages that were suppressed by default.

I played with another solution, see the patch below. It defines
which messages have a valid NOCONS flag according to the msg_seq
number. IMHO, it is a bit more straightforward but it is still
a hack. I am not super happy about it.


Hmm, I seriously think about reverting the commit 375899cddcbb
("printk: make sure to print log on console.") and solving it
another way.

For example, the commit was primary about locations that
wanted to make some messages always visible or always
suppressed. We could create LOG_FORCE_NOCONS and
LOG_FORCE_CONS for these two special cases.



Possible solution: