linux-kernel - Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot reset a storage device

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Message-ID: <CACVXFVN6zm2gG4v1jhV=8EwAtKs=bg3urJ7dRiOgPGHtKXHYxA@mail.gmail.com>
Date:	Mon, 11 Mar 2013 23:52:08 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	ldv-project@...uxtesting.org
Subject: Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot
 reset a storage device

On Mon, Mar 11, 2013 at 11:32 PM, Alan Stern <stern@...land.harvard.edu> wrote:
>
> Of course you have to lock the device before changing its driver.  What
> would happen if two different threads tried to change a device's driver
> at the same time?

Yes, claim/release interface need device lock, but the patch doesn't
touch claim/release command handling.

>
> usbdev_do_ioctl() needs to acquire the device lock in order to prevent
> races with driver_disconnect() and usbdev_remove().

Looks the patch basically converts the allocation inside URB submit path,
and actually I mean why we need to hold device lock in submitting
URB path?  Device lock isn't required before submitting URBs
in kernel driver.


Thanks,
-- 
Ming Lei
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