loop: fix a race when a free loop device is snatched

When /dev/loop-control exists and *device is empty,
the mount may fail if a concurrent mount is running.

function                                             old     new   delta
set_loop                                             809     807      -2

Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed