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Subject: Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation
From:   Oliver Neukum <oneukum@suse.com>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Jaewon Kim <jaewon31.kim@gmail.com>,
        Christoph Hellwig <hch@infradead.org>, linux-mm@kvack.org,
        gregkh@linuxfoundation.org, Jaewon Kim <jaewon31.kim@samsung.com>,
        m.szyprowski@samsung.com, ytk.lee@samsung.com,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Date:   Wed, 22 May 2019 08:31:42 +0200
In-Reply-To: <Pine.LNX.4.44L0.1905210950170.1634-100000@iolanthe.rowland.org>
References: <Pine.LNX.4.44L0.1905210950170.1634-100000@iolanthe.rowland.org>
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On Di, 2019-05-21 at 10:00 -0400, Alan Stern wrote:
> 
> Changing configurations amounts to much the same as disconnecting,
> because both operations destroy all the existing interfaces.
> 
> Disconnect can arise in two different ways.
> 
>         Physical hot-unplug: All I/O operations will fail.
> 
>         Rmmod or unbind: I/O operations will succeed.
> 
> The second case is probably okay.  The first we can do nothing about.  
> However, in either case we do need to make sure that memory allocations
> do not require any writebacks.  This suggests that we need to call
> memalloc_noio_save() from within usb_unbind_interface().

I agree with the problem, but I fail to see why this issue would be
specific to USB. Shouldn't this be done in the device core layer?

	Regards
		Oliver