Describe CVE-2021-47504.
What is CVE-2021-47504?
In the Linux kernel, the following vulnerability has been resolved:

io_uring: ensure task_work gets run as part of cancelations

If we successfully cancel a work item but that work item needs to be
processed through task_work, then we can be sleeping uninterruptibly
in io_uring_cancel_generic() and never process it. Hence we don't
make forward progress and we end up with an uninterruptible sleep
warning.

While in there, correct a comment that should be IFF, not IIF..