linux-kernel - Re: [PATCH] printk: Avoid softlockups in console

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Message-Id: <20130115233742.e8571f92.akpm@linux-foundation.org>
Date:	Tue, 15 Jan 2013 23:37:42 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, jslaby@...e.cz
Subject: Re: [PATCH] printk: Avoid softlockups in console_unlock()

On Tue, 15 Jan 2013 18:58:34 +0100 Jan Kara <jack@...e.cz> wrote:

> A CPU can be caught in console_unlock() for a long time (tens of seconds are
> reported by our customers) when other CPUs are using printk heavily and serial
> console makes printing slow.  This triggers softlockup warnings because
> interrupts are disabled for the whole time console_unlock() runs (e.g.
> vprintk() calls console_unlock() with interrupts disabled).

It should trigger the NMI watchdog in that case?

> We fix the issue by printing at most 1 KB of messages (unless we are in an
> early boot stage or oops is happening) in one console_unlock() call. The rest
> of the buffer will be printed either by further callers to printk() or by a
> queued work.

Complex.  Did you try just putting a touch_nmi_watchdog() in the loop?
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