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 for kexec@lists.infradead.org; Wed, 26 Aug 2020 08:39:09 +0000
From: John Ogness <john.ogness@linutronix.de>
Subject: Re: [PATCH v2 5/7][next] printk: ringbuffer: add
 finalization/extension support
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 <20200824103538.31446-6-john.ogness@linutronix.de>
Date: Wed, 26 Aug 2020 10:45:03 +0206
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To: Petr Mladek <pmladek@suse.com>
Cc: Andrea Parri <parri.andrea@gmail.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Paul McKenney <paulmck@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>

On 2020-08-24, John Ogness <john.ogness@linutronix.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

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