linux-kernel - Re: [PATCH V3] tick/broadcast: Make movement of broadcast hrtimer robust against hotplug

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.11.1501221209260.5526@nanos>
Date:	Thu, 22 Jan 2015 12:15:36 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
cc:	aik@...abs.ru, shreyas@...ux.vnet.ibm.com,
	LKML <linux-kernel@...r.kernel.org>, michael@...erman.id.au,
	Anton Blanchard <anton@...ba.org>, svaidy@...ux.vnet.ibm.com,
	linuxppc-dev@...ts.ozlabs.org,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH V3] tick/broadcast: Make movement of broadcast hrtimer
 robust against hotplug

On Thu, 22 Jan 2015, Preeti U Murthy wrote:
> On 01/21/2015 05:16 PM, Thomas Gleixner wrote:
> How about when the cpu that is going offline receives a timer interrupt
> just before setting its state to CPU_DEAD ? That is still possible right
> given that its clock devices may not have been shutdown and it is
> capable of receiving interrupts for a short duration. Even with the
> above patch, is the following scenario possible ?
> 
>                 CPU0                                  CPU1
> t0         Receives timer interrupt
> 
> t1         Sees that there are hrtimers
>            to be serviced (hrtimers are not yet migrated)
> 
> t2         calls hrtimer_interrupt()
> 
> t3         tick_program_event()                   CPU_DEAD notifiers
>                                                 CPU0's td->evtdev = NULL
> 
> t4         clockevent_program_event()
>            references NULL tick device pointer
> 
> So my concern is that since the CLOCK_EVT_NOTIFY_CPU_DEAD callback
> handles shutting down of devices besides moving tick related duties.
> it's functions may race with the hotplug cpu still handling tick events.

  __cpu_disable() is supposed to block interrupts on the dying cpu.

But I agree, we should make it more robust. So we want an explicit
call for disabling the cpu local stuff and an explicit takeover of the
broadcast duty. I'm anyway distangling the clockevents_notify() stuff,
so it should be simple to do so.

Thanks,

	tglx


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/