linux-kernel - Re: [PATCH] i2c: fix a potential kmemleak of adapter device

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Date:	Tue, 7 Oct 2014 19:34:39 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	linux-i2c@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: fix a potential kmemleak of adapter device

On Mon, Dec 23, 2013 at 09:47:09AM +0800, Gu Zheng wrote:
> Hi Wolfram,
> On 12/21/2013 01:31 AM, Wolfram Sang wrote:
> 
> > On Wed, Dec 18, 2013 at 09:18:08AM +0800, Gu Zheng wrote:
> >> When running with the latest kernel, we get the following kmemleak message:
> >> unreferenced object 0xffff8800c2a36100 (size 256):
> >>   comm "modprobe", pid 629, jiffies 4294676002 (age 1531.115s)
> >>   hex dump (first 32 bytes):
> >>     00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
> >>     ff ff ff ff ff ff ff ff 78 21 85 82 ff ff ff ff  ........x!......
> >>   backtrace:
> >>     [<ffffffff815449ce>] kmemleak_alloc+0x73/0x98
> >>     [<ffffffff8113fa2b>] slab_post_alloc_hook+0x28/0x2a
> >>     [<ffffffff81142004>] __kmalloc+0x12c/0x158
> >>     [<ffffffff8134c60b>] kzalloc.constprop.6+0xe/0x10
> >>     [<ffffffff8134cb71>] device_private_init+0x18/0x66
> >>     [<ffffffff8134f1e8>] dev_set_drvdata+0x1e/0x34
> >>     [<ffffffffa01e643e>] i801_probe+0x5d/0x447 [i2c_i801]
> >>     [<ffffffff812a78be>] local_pci_probe+0x41/0x84
> >>     [<ffffffff812a7feb>] pci_device_probe+0xdf/0x10c
> >>     [<ffffffff8134f90d>] driver_probe_device+0x12f/0x2ee
> >>     [<ffffffff8134fb2b>] __driver_attach+0x5f/0x83
> >>     [<ffffffff8134de28>] bus_for_each_dev+0x64/0x90
> >>     [<ffffffff8134f36b>] driver_attach+0x1e/0x20
> >>     [<ffffffff8134ef34>] bus_add_driver+0xf2/0x1f0
> >>     [<ffffffff8135013e>] driver_register+0x8c/0xc3
> >>     [<ffffffff812a7bb4>] __pci_register_driver+0x62/0x67
> >> According to the backtrace, it seems that we do not release the
> >> device_private field of adapter device in the fail path of i801_probe
> >> or the flow of i2c_del_adapter, so add the cleanup step to fix it.
> >>
> >> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
> > 
> > ? Why should we free something we don't have allocated? The fix must be
> > somewhere else probably...
> 
> We do allocate the device_private in device_private_init() when calling
> dev_set_drvdata()

dev_set_drvdata only does the following and doesn't call anything:

	dev->driver_data = data;

> to set adapter data in probe flow, and the calltrace
> also shows this. Am I missing something?

It should be freed by the driver core in device_release() again. Dunno
why it does not happen and you are seeing the leak, but the fix is not
correct.


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