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Date:   Mon, 20 Nov 2023 14:45:56 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, Mukesh Ojha <quic_mojha@quicinc.com>
Subject: Re: [PATCH printk v2 1/9] printk: ringbuffer: Do not skip
 non-finalized records with prb_next_seq()
Message-ID: <20231120134556.DkKNwy7B@linutronix.de>
References: <20231106210730.115192-1-john.ogness@linutronix.de>
 <20231106210730.115192-2-john.ogness@linutronix.de>
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In-Reply-To: <20231106210730.115192-2-john.ogness@linutronix.de>
Precedence: bulk

based on my research this should be the most recent post of this patch.
If so then

On 2023-11-06 22:13:22 [+0106], John Ogness wrote:
> --- a/kernel/printk/printk_ringbuffer.c
> +++ b/kernel/printk/printk_ringbuffer.c
> @@ -6,6 +6,7 @@
> @@ -1441,20 +1445,144 @@ bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer
>  	return false;
>  }
>  
> +#ifdef CONFIG_64BIT
> +
> +#define __u64seq_to_ulseq(u64seq) (u64seq)
> +#define __ulseq_to_u64seq(ulseq) (ulseq)
> +
> +#else /* CONFIG_64BIT */
> +
> +static u64 prb_first_seq(struct printk_ringbuffer *rb);
> +
> +#define __u64seq_to_ulseq(u64seq) ((u32)u64seq)
> +static inline u64 __ulseq_to_u64seq(u32 ulseq)
> +{
> +	u64 rb_first_seq = prb_first_seq(prb);
> +	u64 seq;
> +
> +	/*
> +	 * The provided sequence is only the lower 32 bits of the ringbuffer
> +	 * sequence. It needs to be expanded to 64bit. Get the first sequence
> +	 * number from the ringbuffer and fold it.
> +	 */
> +	seq = rb_first_seq - ((u32)rb_first_seq - ulseq);

This needs to become
	seq = rb_first_seq - ((s32)((u32)rb_first_seq - ulseq));

in order to continue booting on 32bit. Otherwise, if this survives one
cycle then we can deprecate all 32bit platforms. I am happy either way.

Sebastian