Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

On Wednesday 10 October 2012 11:19:09 Ming Lei wrote:

On Tue, Oct 9, 2012 at 4:47 PM, Oliver Neukum [off-list ref] wrote:

quoted

Using GFP_KERNEL you preclude using those in resume() and error handling.
Please pass a gfp_t parameter.

IMO, it is not a big deal because generally only several bytes are to be
allocated inside these helpers.

Any allocation can do it, if the VM layer decides to block.

If you still think the problem should be considered, another candidate fix
is to take GFP_NOIO during system suspend/resume, and take GFP_KERNEL
in other situations.

No, the problem is autoresume.

Suppose we have a device with two interface. Interface A be usbnet; interface B
something you page on. Now consider that you can only resume both interfaces
and this is (and needs to be) done synchronously.

Now we can have this code path:

autoresume of device -> resume() -> kmalloc(..., GFP_KERNEL) ->
VM layer decides to start paging out -> IO to interface B -> autoresume of device
--> DEADLOCK

We need to use GFP_NOIO in situations the helper cannot know about.
Please add a gfp_t parameter. Then the caller will solve that.

	Regards
		Oliver

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