linux-kernel - Re: [ANNOUNCE] v6.3-rc2-rt3

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Date:   Fri, 14 Apr 2023 17:38:56 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     John Ogness <john.ogness@...utronix.de>,
        Pierre Gondois <pierre.gondois@....com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [ANNOUNCE] v6.3-rc2-rt3

On 4/14/23 17:01, John Ogness wrote:
> On 2023-04-14, Vlastimil Babka <vbabka@...e.cz> wrote:
>> Is it perhaps a similar situation to this thread?
>>
>> https://lore.kernel.org/all/20230412124735.GE628377@hirez.programming.kicks-ass.net/
> 
> We are dealing with a spin_lock() inside a raw_spin_lock() section. The
> legacy console drivers do this. The fix is the new atomic/threaded
> consoles. For CONFIG_PREEMPT_RT a workaround is implemented so that the
> legacy consoles avoid this. For !CONFIG_PREEMPT_RT you can expect
> CONFIG_PROVE_RAW_LOCK_NESTING to cause a splat on that printk().
> 
> Or perhaps that particular printk() in cblist_init_generic() should be
> changed to printk_deferred() as a temporary whack-a-mole
> workaround.

What I meant that in the linked thread a solution seems to be forming in the
form of annotation for lockdep/CONFIG_PROVE_RAW_LOCK_NESTING to make it
aware that on CONFIG_PREEMPT_RT the problem it sees is side-stepped so it
shouldn't warn about it on !PREEMPT_RT, and maybe that solution could be
used for the printk issue as well (I admit I didn't check the code, just by
reading your mail it sounded very similar).

> John Ogness