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

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Date:	Thu, 7 Nov 2013 00:27:56 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	"dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
	"tj@...nel.org" <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] devres: Freeing the drs after all release() are called

Hello Greg,

> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Wednesday, November 06, 2013 4:59 PM
> To: Liu, Chuansheng
> Cc: dmitry.torokhov@...il.com; tj@...nel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] devres: Freeing the drs after all release() are called
> 
> On Wed, Nov 06, 2013 at 02:40:18PM +0800, Chuansheng Liu wrote:
> >
> > In release_nodes(), it will call dr->node.release() and kfree
> > dr one by one.
> >
> > But sometimes the previous dr maybe be used by next .release(),
> > such as:
> > [50314.855534]  [<c12b172f>] ? synchronize_irq+0x3f/0xb0
> > [50314.861193]  [<c12b18e9>] __free_irq+0x149/0x200
> > [50314.866367]  [<c12b19e3>] free_irq+0x43/0xa0
> > [50314.871152]  [<c12b4864>] devm_irq_release+0x14/0x20
> > [50314.876713]  [<c169e806>] release_nodes+0x136/0x1b0
> > [50314.882178]  [<c169ee79>] devres_release_all+0x39/0x60
> > [50314.887935]  [<c169b411>] __device_release_driver+0x71/0xd0
> >
> > the free_irq() will sync the last irq handling, which maybe use
> > freed dr, then it will cause memory corruption.
> >
> > Here split the dr kfreeing actions after all dr->node.release().
> 
> But you aren't really solving any problems here, how is dr being used
> after the release function is called?  Who is doing it in such a way
> that this change would really fix anything?
> 
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.
Thanks.



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