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From: Tvrtko Ursulin <tursulin@ursulin.net>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH] cpu/hotplug: Reset node state after operation
Date: Mon, 23 Oct 2017 09:01:44 +0100	[thread overview]
Message-ID: <898ff90e-3462-6802-8c7b-6f3e8e272ce7@ursulin.net> (raw)
In-Reply-To: <alpine.DEB.2.20.1710211606130.3213@nanos>


On 21/10/17 15:06, Thomas Gleixner wrote:
> The recent rework of the cpu hotplug internals changed the usage of the per
> cpu state->node field, but missed to clean it up after usage.
> 
> So subsequent hotplug operations use the stale pointer from a previous
> operation and hand it into the callback functions. The callbacks then
> dereference a pointer which either belongs to a different facility or
> points to freed and potentially reused memory. In either case data
> corruption and crashes are the obvious consequence.
> 
> Reset the node and the last pointers in the per cpu state to NULL after the
> operation which set them has completed.
> 
> Fixes: 96abb968549c ("smp/hotplug: Allow external multi-instance rollback")
> Reported-by: Tvrtko Ursulin <tursulin@ursulin.net>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>   kernel/cpu.c |    5 +++++
>   1 file changed, 5 insertions(+)
> 
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -632,6 +632,11 @@ cpuhp_invoke_ap_callback(int cpu, enum c
>   		__cpuhp_kick_ap(st);
>   	}
>   
> +	/*
> +	 * Clean up the leftovers so the next hotplug operation wont use stale
> +	 * data.
> +	 */
> +	st->node = st->last = NULL;
>   	return ret;
>   }
>   
> 

Our CI farm is happy with this fix, so:

Tested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Thanks for looking into is so quickly!

Regards,

Tvrtko

      parent reply	other threads:[~2017-10-23  8:01 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-21 14:06 Thomas Gleixner
2017-10-21 14:16 ` [tip:smp/urgent] " tip-bot for Thomas Gleixner
2017-10-22  2:49 ` [PATCH] " Paul E. McKenney
2017-10-22  9:22 ` Peter Zijlstra
2017-10-23  8:01 ` Tvrtko Ursulin [this message]

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