linux-kernel - Re: [PATCH] percpu: use notrace variant of preempt_disable/preempt

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Message-Id: <20161108105655.129ee2d7@mschwide>
Date:   Tue, 8 Nov 2016 10:56:55 +0100
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        Sebastian Ott <sebott@...ux.vnet.ibm.com>
Subject: Re: [PATCH] percpu: use notrace variant of
 preempt_disable/preempt_enable

On Mon, 7 Nov 2016 12:27:16 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 3 Nov 2016 14:58:38 +0100
> Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> 
> > Commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like
> > events do") added a couple of this_cpu_read calls to the ftrace code.
> > 
> > On x86 this is not a problem, since it has single instructions to read
> > percpu data. Other architectures which use the generic variant now
> > have additional preempt_disable and preempt_enable calls in the core
> > ftrace code. This may lead to recursive calls and in result to a dead
> > machine, e.g. if preemption and debugging options are enabled.
> > 
> > To fix this use the notrace variant of preempt_disable and
> > preempt_enable within the generic percpu code.
> > 
> > Reported-and-bisected-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> > Tested-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> > Fixes: 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like events do")
> > Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> Acked-by: Steven Rostedt <rostedt@...dmis.org>
> 
> Feel free to push this in your tree.

Ok, will do. Thanks.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.