linux-kernel - Re: printk: selective deactivation of feature ignoring non panic cpu's messages

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Message-ID: <20250317050657.GA693154@tiffany>
Date: Mon, 17 Mar 2025 14:06:57 +0900
From: Donghyeok Choe <d7271.choe@...sung.com>
To: Petr Mladek <pmladek@...e.com>
Cc: linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	john.ogness@...utronix.de, senozhatsky@...omium.org, takakura@...inux.co.jp,
	youngmin.nam@...sung.com, hajun.sung@...sung.com, seungh.jung@...sung.com,
	jh1012.choi@...sung.com, d7271.choe@...sung.com
Subject: Re: printk: selective deactivation of feature ignoring non panic
 cpu's messages

On Tue, Mar 04, 2025 at 03:15:46PM +0100, Petr Mladek wrote:
> On Tue 2025-03-04 15:05:52, John Ogness wrote:
> > On 2025-03-04, Petr Mladek <pmladek@...e.com> wrote:
> > > I mean something like:
> > >
> > > --- a/kernel/printk/printk_ringbuffer.c
> > > +++ b/kernel/printk/printk_ringbuffer.c
> > > @@ -2143,7 +2143,9 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
> > >  			 * But it would have the sequence number returned
> > >  			 * by "prb_next_reserve_seq() - 1".
> > >  			 */
> > > -			if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb)))
> > > +			if (this_cpu_in_panic() &&
> > > +			    (!printk_debug_non_panic_cpus || legacy_allow_panic_sync) &&
> > > +			    ((*seq + 1) < prb_next_reserve_seq(rb)))
> > >  				(*seq)++;
> > >  			else
> > >  				return false;
> > 
> > Ah, OK. Thanks for the clarification
> > 
> > > OK, I propose the following changes:
> > >
> > >   + rename the option to "printk_debug_non_panic_cpus"
> > >
> > >   + do not skip the messages in _prb_read_valid() when this option
> > >     is used before the non-panic CPUs are stopped.
> > 
> > And of course:
> > 
> >     + allow non-panic CPUs in panic to store messages when this option
> >       is set
> > I would also keep the dump_stack_lvl() implementation as it is, even if
> > it could lead to interweaving of backtraces. Anyone using
> > printk_debug_non_panic_cpus should have CONFIG_PRINTK_CALLER enabled.


Hi Petr Mladek,

This is gentle remind.

I did upload the patch containing the above contents.
Link: https://lore.kernel.org/all/20250305044046.1249972-1-d7271.choe@samsung.com/

Even if it's not necessarily this patch, I hope the content will be applied.
When can the 'printk_debug_non_panic_cpus' function be reflected
in mainline source code?


Thanks.