io-wq: check for wq exit after adding new worker task_work

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: io-wq: check for wq exit after adding new worker task_work We check IO_WQ_BIT_EXIT before attempting to create a new worker, and wq exit cancels pending work if we have any. But it's possible to have a race between the two, where creation checks exit finding it not set, but we're in the process of exiting. The exit side will cancel pending creation task_work, but there's a gap where we add task_work after we've canceled existing creations at exit time. Fix this by checking the EXIT bit post adding the creation task_work. If it's set, run the same cancelation that exit does.

References

• https://git.kernel.org/stable/c/4b4e5bbf9386d4ec21d91c0cb0fd60b9bba778ec
• https://git.kernel.org/stable/c/71a85387546e50b1a37b0fa45dadcae3bfb35cf6