linux-kernel - Re: [PATCH] devres: Freeing the drs after all release() are called

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Message-ID: <20131107004659.GA3312@core.coreip.homeip.net>
Date:	Wed, 6 Nov 2013 16:46:59 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc:	"tj@...nel.org" <tj@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devres: Freeing the drs after all release() are called

On Thu, Nov 07, 2013 at 12:36:56AM +0000, Liu, Chuansheng wrote:
> 
> 
> > -----Original Message-----
> > From: Tejun Heo [mailto:htejun@...il.com] On Behalf Of tj@...nel.org
> > Sent: Thursday, November 07, 2013 8:30 AM
> > To: Liu, Chuansheng
> > Cc: Greg KH; dmitry.torokhov@...il.com; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] devres: Freeing the drs after all release() are called
> > 
> > Hello, Liu.
> > 
> > On Thu, Nov 07, 2013 at 12:27:56AM +0000, Liu, Chuansheng wrote:
> > > The driver code is as below:
> > > _INIT() {
> > >
> > > A = devm_kzalloc();
> > > B= devm_request_threaded_irq(isr_handler);
> > > C = devm_kzalloc();
> > > }
> > >
> > > When driver _EXIT, the devres_release_all () will be called.
> > > The C will be kfreed before B, but when freeing irq B, the pending isr_handler()
> > possibly
> > > will access the memory B which has been freed.
> > > Then the memory corruption occurred.
> > >
> > > This patch can solve this scenario.
> > 
> > Isn't the bug there IRQ being requested before all its resources are
> > allocated?  The proposed change just masks the underlying issue or
> > incorrectly ordered operations.
> Yes, I knew I can put the code always like below:
> A = devm_kzalloc();
> C = devm_kzalloc();
> ...
> B= devm_request_threaded_irq(isr_handler);
> 
> But, the above is just one simple coding prototype, if there are many calling:
> E -- > F -- > D -- >... then to devm_kzalloc().
> 
> To be honest, it will make code too hard to always adapt the rule?
> And I trying to find out every potential devm_kzalloc() before irq requesting.

Such code is already broken anyway and has to be fixed - if your IRQ
handler accesses data allocated by devm_kzalloc that you call only
_after_ you called devm_request_irq() then interrupt arriving at
unfortunate moment will crash your driver at the probing stage.

Thanks. 

-- 
Dmitry
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