Messages in this thread | | | Date | Mon, 11 Mar 2013 12:08:46 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot reset a storage device |
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On Mon, 11 Mar 2013, Ming Lei wrote:
> On Mon, Mar 11, 2013 at 11:32 PM, Alan Stern <stern@rowland.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.
Then why did you ask? You wrote: "Looks device lock isn't required for USB transfer of kernel driver."
> > 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.
In general it isn't, no. But usbfs uses the lock to prevent races with driver_disconnect() -- it is invalid to submit URBs after the disconnect routine has returned.
Alan Stern
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