Commit adeaa3f2 authored Jun 13, 2023 by Jens Axboe

io_uring/io-wq: clear current->worker_private on exit



A recent fix stopped clearing PF_IO_WORKER from current->flags on exit,
which meant that we can now call inc/dec running on the worker after it
has been removed if it ends up scheduling in/out as part of exit.

If this happens after an RCU grace period has passed, then the struct
pointed to by current->worker_private may have been freed, and we can
now be accessing memory that is freed.

Ensure this doesn't happen by clearing the task worker_private field.
Both io_wq_worker_running() and io_wq_worker_sleeping() check this
field before going any further, and we don't need any accounting etc
done after this worker has exited.

Fixes: fd37b884 ("io_uring/io-wq: don't clear PF_IO_WORKER on exit")
Reported-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent cac9e441

io_uring/io-wq.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -220,7 +220,12 @@ static void io_worker_exit(struct io_worker *worker)
		list_del_rcu(&worker->all_list);
		raw_spin_unlock(&wq->lock);
		io_wq_dec_running(worker);
		worker->flags = 0;
		/*
		* this worker is a goner, clear ->worker_private to avoid any
		* inc/dec running calls that could happen as part of exit from
		* touching 'worker'.
		*/
		current->worker_private = NULL;

		kfree_rcu(worker, rcu);
		io_worker_ref_put(wq);