On Thu, Sep 27, 2012 at 8:24 PM, Yasuaki Ishimatsu
[off-list ref] wrote:

Hi Chen,


2012/09/27 19:20, Ni zhan Chen wrote:

quoted

Hi Congyang,

2012/9/27 [off-list ref]

quoted

From: Yasuaki Ishimatsu <redacted>

When calling remove_memory_block(), the function shows following message
at
device_release().

Device 'memory528' does not have a release() function, it is broken and
must
be fixed.

What's the difference between the patch and original implemetation?

The implementation is for removing a memory_block. So the purpose is
same as original one. But original code is bad manner. kobject_cleanup()
is called by remove_memory_block() at last. But release function for
releasing memory_block is not registered. As a result, the kernel message
is shown. IMHO, memory_block should be release by the releae function.

but your patch introduced use after free bug, if i understand correctly.
See unregister_memory() function. After your patch, kobject_put() call
release_memory_block() and kfree(). and then device_unregister() will
touch freed memory.

static void
unregister_memory(struct memory_block *memory)
{
	BUG_ON(memory->dev.bus != &memory_subsys);

	/* drop the ref. we got in remove_memory_block() */
	kobject_put(&memory->dev.kobj);
	device_unregister(&memory->dev);
}

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