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From:   "Liu, Chuansheng" <chuansheng.liu@intel.com>
To:     Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Luck, Tony" <tony.luck@intel.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "hpa@zytor.com" <hpa@zytor.com>
Subject: RE: [PATCH] x86/mce/therm_throt: Fix the access of uninitialized
 therm_work
Thread-Topic: [PATCH] x86/mce/therm_throt: Fix the access of uninitialized
 therm_work
Thread-Index: AQHVxFzlxQRcQtSYTE6XKuL77zdvEafcsTeAgAAA4ICACDBbgA==
Date:   Sat, 11 Jan 2020 04:20:02 +0000
Message-ID: <27240C0AC20F114CBF8149A2696CBE4A61601F7D@SHSMSX101.ccr.corp.intel.com>
References: <20200106064155.64-1-chuansheng.liu@intel.com>
 <20200106070759.GB12238@zn.tnic> <20200106071107.GA95725@gmail.com>
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Hi Ingo,

> -----Original Message-----
> From: Ingo Molnar <mingo.kernel.org@gmail.com> On Behalf Of Ingo Molnar
> Sent: Monday, January 6, 2020 3:11 PM
> To: Borislav Petkov <bp@alien8.de>
> Cc: Liu, Chuansheng <chuansheng.liu@intel.com>; linux-kernel@vger.kernel.org;
> Luck, Tony <tony.luck@intel.com>; tglx@linutronix.de; mingo@redhat.com;
> hpa@zytor.com
> Subject: Re: [PATCH] x86/mce/therm_throt: Fix the access of uninitialized
> therm_work
> 
> * Borislav Petkov <bp@alien8.de> wrote:
> 
> > On Mon, Jan 06, 2020 at 06:41:55AM +0000, Chuansheng Liu wrote:
> > > In ICL platform, it is easy to hit bootup failure with panic
> > > in thermal interrupt handler during early bootup stage.
> > >
> > > Such issue makes my platform almost can not boot up with
> > > latest kernel code.
> > >
> > > The call stack is like:
> > > kernel BUG at kernel/timer/timer.c:1152!
> > >
> > > Call Trace:
> > > __queue_delayed_work
> > > queue_delayed_work_on
> > > therm_throt_process
> > > intel_thermal_interrupt
> > > ...
> > >
> > > When one CPU is up, the irq is enabled prior to CPU UP
> > > notification which will then initialize therm_worker.
> >
> > You mean the unmasking of the thermal vector at the end of
> > intel_init_thermal()?
> >
> > If so, why don't you move that to the end of the notifier and unmask it
> > only after all the necessary work like setting up the workqueues etc, is
> > done, and save yourself adding yet another silly bool?
> 
> A debugging WARN_ON_ONCE() when the workqueue is not initialized yet
> would also be useful I suspect. This would turn any remaining race-crash
> boot failure in this area into a warning.
> 
Just checked the code, the WARN_ON_ONCE() is already there:
1622         WARN_ON_ONCE(timer->function != delayed_work_timer_fn);

With reproducing it, the corresponding log also shows before panic:
WARNING: CPU: 0 .... at kernel/workqueue.c:1622 __queue_delayed_work+0x73/0x90

Thanks for your reminder.