rfkill: fix rfkill_fop_read wait_event usage
commit 6736fde9 upstream. The code within wait_event_interruptible() is called with !TASK_RUNNING, so mustn't call any functions that can sleep, like mutex_lock(). Since we re-check the list_empty() in a loop after the wait, it's safe to simply use list_empty() without locking. This bug has existed forever, but was only discovered now because all userspace implementations, including the default 'rfkill' tool, use poll() or select() to get a readable fd before attempting to read. Fixes: c64fb016 ("rfkill: create useful userspace interface") Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
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