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Date:   Tue, 6 Jun 2023 11:48:55 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        stable-rt <stable-rt@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Carsten Emde <C.Emde@osadl.org>,
        Daniel Wagner <daniel.wagner@suse.com>,
        Tom Zanussi <tom.zanussi@linux.intel.com>,
        Clark Williams <williams@redhat.com>,
        Mark Gross <markgross@kernel.org>,
        Pavel Machek <pavel@denx.de>,
        Jeff Brady <jeffreyjbrady@gmail.com>
Subject: Re: [ANNOUNCE] 5.10.180-rt88
Message-ID: <20230606094855.v8zhk78I@linutronix.de>
References: <ZHZSlJFnTK1IpXeg@uudg.org>
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On 2023-05-30 16:46:28 [-0300], Luis Claudio R. Goncalves wrote:
> Hello RT-list!
Hi,

> Support for deferred printing was removed in v5.10-rc1-rt1 by commit
> 9153e3c5cb0c9 ("printk: remove deferred printing").

Sorry for not getting back to earlier, where you proposed the change.

> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 83c7734e98025..92e0656841128 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -609,7 +609,7 @@ static inline void print_hex_dump_debug(const char *prefix_str, int prefix_type,
>  #define print_hex_dump_bytes(prefix_str, prefix_type, buf, len)	\
>  	print_hex_dump_debug(prefix_str, prefix_type, 16, 1, buf, len, true)
>  
> -#ifdef CONFIG_PRINTK
> +#if defined(CONFIG_PRINTK) && !defined(CONFIG_PREEMPT_RT)
>  extern void __printk_safe_enter(void);
>  extern void __printk_safe_exit(void);

This needs to go entirely. The "new" printk code does not need this safe
functions also for !RT.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5f1c50a6bebc5..7e65e3ef16e3a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6057,7 +6057,6 @@ static void __build_all_zonelists(void *data)
>  	 * tty_insert_flip_string_and_push_buffer() on other CPU might be
>  	 * calling kmalloc(GFP_ATOMIC | __GFP_NOWARN) with port->lock held.
>  	 */
> -	printk_deferred_enter();

That is okay. However the commit, that introduced this
	a992c387b4118 ("mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock")

also added a local_irq_safe a little higher up and it has to go, too.
The code as-is should produce warnings once it enters this path.

>  	write_seqlock(&zonelist_update_seq);
>  
>  #ifdef CONFIG_NUMA

Sebastian