On Sun, Mar 27, 2022 at 02:25:01AM +0200, Tasos Sahanidis wrote:
> Since commit ae8709b296d8 ("USB: core: Make do_proc_control() and
> do_proc_bulk() killable") if a device has the USB_QUIRK_DELAY_CTRL_MSG
> quirk set, it will temporarily block all other URBs (e.g. interrupts)
> while sleeping due to a control.
>
> This results in noticeable delays when, for example, a userspace usbfs
> application is sending URB interrupts at a high rate to a keyboard and
> simultaneously updates the lock indicators using controls. Interrupts
> with direction set to IN are also affected by this, meaning that
> delivery of HID reports (containing scancodes) to the usbfs application
> is delayed as well.
>
> This patch fixes the regression by calling msleep() while the device
> mutex is unlocked, as was the case originally with usb_control_msg().
>
> Fixes: ae8709b296d8 ("USB: core: Make do_proc_control() and do_proc_bulk() killable")
> Signed-off-by: Tasos Sahanidis <tasos@xxxxxxxxxxxx>
> ---
Thanks for identifying and fixing this.
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
You might want to change the patch name, however. "Block" usually means
pretty much the same thing as "sleep"; i.e., a process is blocked if it
can't move forward. The name should be something like "Don't hold the
device lock while sleeping in do_proc_control()".
Alan Stern
