linux-kernel - Re: [PATCH v2 5/7][next] printk: ringbuffer: add finalization/extension support

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Date:   Wed, 26 Aug 2020 10:45:03 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Paul McKenney <paulmck@...nel.org>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7][next] printk: ringbuffer: add finalization/extension support

On 2020-08-24, John Ogness <john.ogness@...utronix.de> wrote:
> @@ -1157,6 +1431,14 @@ bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
>  		goto fail;
>  	}
>  
> +	/*
> +	 * New data is about to be reserved. Once that happens, previous
> +	 * descriptors are no longer able to be extended. Finalize the
> +	 * previous descriptor now so that it can be made available to
> +	 * readers (when committed).
> +	 */
> +	desc_finalize(desc_ring, DESC_ID(id - 1));
> +
>  	d = to_desc(desc_ring, id);
>  
>  	/*

Apparently this is not enough to guarantee that past descriptors are
finalized. I am able to reproduce a scenario where the finalization of a
certain descriptor never happens. That leaves the descriptor permanently
in the reserved queried state, which prevents any new records from being
created. I am investigating.

John Ogness