linux-kernel - Re: [PATCH -rt] printk: Don't emit console_cpu_notify() for CPU

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Message-ID: <20111117052906.GC14492@zhy>
Date:	Thu, 17 Nov 2011 13:29:06 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH -rt] printk: Don't emit console_cpu_notify() for CPU_DYING

On Wed, Nov 16, 2011 at 03:48:11PM +0100, Thomas Gleixner wrote:
> On Wed, 16 Nov 2011, Steven Rostedt wrote:
> > Thomas, doesn't printk not print to serial in atomic contexts? Or did

I guess you mean console_trylock_for_printk() will fail in atomic context?
If so, yeah, that doesn't change.

But the issue is console_cpu_notify() call console_lock() directly.
That means below scenario could also happen in mainline:

	CPU A				CPU B

doing printk with console_sem held
				take_cpu_down();
				  cpu_notify(CPU_DYING);
				    console_cpu_notify();
				      console_lock();
				        down(&console_sem);
					  *bang*
  up(&console_sem);

Sounds I should also send this patch to mainline.

Thanks,
Yong
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