On Fri, 18 Jan 2013, Sergei Shtylyov wrote:
> Serialize usb-storage operations with usbfs and 'cat /proc/bus/usb/devices',
> so that they cannot disturb storage by seemingly harmless control reads.
>
> This patch was adapted from 2.4 patches by Pete Zaitcev. The initial patch of
> the series dates back to 2004 and it unfortunately wasn't applied to 2.6 in
> the
> same form back then (it was applied in another form and immediately reverted).
> Despite 8+ years passing from that moment, the vendors didn't stop producing
> USB devices that require this kind of patch. Two recent examples are SanDisk
> Cruzer Slice 8GB and Kingston DataTraveller 100 G2 32GB. In the latter case,
> even the enumeration fails as the INQUIRY command normally takes 2.8 seconds
> to
> finish, so 'udev' also comes into action with its control requests, with
> neither
> completing normally.
>
> Signed-off-by: Sergei Shtylyov <sshtyl...@ru.mvista.com>
> Cc: sta...@vger.kernel.org
Assuming Greg ever agrees to merge this, I will insist on a few
changes.
> --- usb.orig/include/linux/usb.h
> +++ usb/include/linux/usb.h
> @@ -439,6 +439,13 @@ struct usb3_lpm_parameters {
> * @speed: device speed: high/full/low (or error)
> * @tt: Transaction Translator info; used with low/full speed dev, highspeed
> hub
> * @ttport: device port on that tt hub
> + * @excl_wait: wait queue used to wait on @excl_type
> + * @excl_lock: spinlock guarding @excl_type
> + * @excl_type: exclusion lock type:
> + * 0 - unlocked
> + * 1 - locked for reads
> + * 2 - locked for writes
> + * 3 - locked for everything
Magic numbers like this are a terrible idea. Use an enumeration type
instead. And instead of using 0 or 1 for the "interruptible" argument,
use TASK_UNINTERRUPTIBLE or TASK_INTERRUPTIBLE. Better yet, have
separate "lock" and "lock_interruptible" functions.
Furthermore, the locking in usbfs doesn't look right. A process should
be able to submit as many URBs as it wants, of whatever type, at any
time. The locking should be by file handle, not by "read" vs. "write".
Alan Stern
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