linux-kernel - Re: [PATCH 1/3] context_tracking: Protect against recursion

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Message-ID: <551D83DD.5010200@redhat.com>
Date:	Thu, 02 Apr 2015 14:01:01 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/3] context_tracking: Protect against recursion

On 04/02/2015 01:39 PM, Frederic Weisbecker wrote:
> Context tracking recursion can happen when an exception triggers in the
> middle of a call to a context tracking probe.
> 
> This special case can be caused by vmalloc faults. If an access to a
> memory area allocated by vmalloc happens in the middle of
> context_tracking_enter(), we may run into an endless fault loop because
> the exception in turn calls context_tracking_enter() which faults on
> the same vmalloc'ed memory, triggering an exception again, etc...
> 
> Some rare crashes have been reported so lets protect against this with
> a recursion counter.
> 
> Reported-by: Dave Jones <davej@...hat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Dave Jones <davej@...hat.com>
> Cc: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Rik van Riel <riel@...hat.com>

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