In the Linux kernel, the following vulnerability has been resolved:io_uring: check if iowq is killed before queuingtask work can be executed after the task has gone through io_uringtermination, whether it's the final task_work run or the fallback path.In this case, task work will find ->io_wq being already killed andnull'ed, which is a problem if it then tries to forward the request toio_queue_iowq(). Make io_queue_iowq() fail requests in this case.Note that it also checks PF_KTHREAD, because the user can first closea DEFER_TASKRUN ring and shortly after kill the task, in which case->iowq check would race.
