linux-kernel - Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async

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Date:	Tue, 22 Mar 2016 14:52:43 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Petr Mladek <pmladek@...e.com>,
	Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async

On (03/22/16 11:13), Byungchul Park wrote:
[..]

what about a "normal" case, when things are not going to explode printk(),
but we have several lockups on the same lock (which is probably more
likely than printk recursion)?

suppose:
- there are 8 CPUs on the system
- 1 cpus owns the spin_lock for too long
- 4 cpus are trying to lock the spin_lock w/o any success
- so all 4 trigger spin_dump.

what we have at the moment, is that all 4 CPUs will report a lockup,
but with this static pointer only X (between 1 and 4, depending on the
timing; on how fast spin_dump() will return (logbuf lock can
be busy for a while); etc.) CPUs will do so.

	-ss