linux-kernel - Re: Strange hang on ia64 with CONFIG_PRINTK

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Date:	Tue, 19 Feb 2008 14:40:35 -0800
From:	"Tony Luck" <tony.luck@...il.com>
To:	"Roland Dreier" <rdreier@...co.com>
Cc:	"David Miller" <davem@...emloft.net>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: Strange hang on ia64 with CONFIG_PRINTK_TIME=y

> Perhaps what is happening is that cpu0 comes online ... safely skips
> over the early printk calls.  Calls cpu_init() which sets up the resources
> *it* needs (ar.k3 points to per-cpu space), and then executes
> sched_init() which marks it safe for all printk's. Then cpu1 comes
> up and does a printk before it gets to cpu_init().

I just tried Ingo's patch[1] on a 2.6.25-rc2 kernel with printk timestamps
turned on ... and it booted just fine on my tiger4.  The default path
for non-boot cpus is from head.S to start_secondary(), and that
calls cpu_init() pretty quickly.  There shouldn't normally[2] be any
printk() calls on the non-boot cpu before it is safe to do so.

-Tony

[1] Attached
[2] If you set #define SMP_DEBUG in arch/ia64/kernel/smpboot.c
that enables at least one printk() that will cause problems if you have
also configured timestamps.

View attachment "ingo.patch" of type "text/x-patch" (1271 bytes)