usb: using mutex lock and supporting O_NONBLOCK flag in iowarrior_read()

usb: using mutex lock and supporting O_NONBLOCK flag in iowarrior_read()

iowarrior_read() uses the iowarrior dev structure, but does not use any
lock on the structure. This can cause various bugs including data-races,
so it is more appropriate to use a mutex lock to safely protect the
iowarrior dev structure. When using a mutex lock, you should split the
branch to prevent blocking when the O_NONBLOCK flag is set.

In addition, it is unnecessary to check for NULL on the iowarrior dev
structure obtained by reading file->private_data. Therefore, it is
better to remove the check.

Fixes: 946b960d13c1 ("USB: add driver for iowarrior devices.")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Link: https://lore.kernel.org/r/20240919103403.3986-1-aha310510@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>