linux-kernel - Re: [PATCH v2 2/2] MIPS: fix kernel lockup or crash after CPU offline/online

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Date:	Fri, 30 Jan 2015 18:53:56 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	James Hogan <james.hogan@...tec.com>
cc:	Aaro Koskinen <aaro.koskinen@....fi>,
	Ralf Baechle <ralf@...ux-mips.org>,
	David Daney <david.daney@...ium.com>,
	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	Hemmo Nieminen <hemmo.nieminen@....fi>, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] MIPS: fix kernel lockup or crash after CPU
 offline/online

On Fri, 30 Jan 2015, James Hogan wrote:

> > > Hmm, kernel/printk/printk.c does have:
> > > 
> > > static inline int can_use_console(unsigned int cpu)
> > > {
> > > 	return cpu_online(cpu) || have_callable_console();
> > > }
> > > 
> > > which should prevent it dumping printk buffer to console. CPU shouldn't
> > > be marked online that early, which suggests that the console has the
> > > CON_ANYTIME flag set, which it probably shouldn't if it depends on
> > > module code. call_console_drivers() seems to ensure the CPU is online or
> > > has CON_ANYTIME before calling the console write callback.
> > > 
> > > A quick glance and I can't see any evidence of netconsole being able to
> > > get CON_ANYTIME.
> > 
> > It does not set the flag. But flags are kept in module's static data,
> > so the original problem stays.
> > 
> > A.
> 
> Ah yes, of course. This approach looks correct to me then.

 In such a case shouldn't the flags be copied out on console registration 
to a structure that is guaranteed to be accessible at all times?

  Maciej
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