From adeaa3f290ecf7f6a6a5c53219a4686cbdff5fbd Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 13 Jun 2023 19:26:55 -0600 Subject: [PATCH] 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: fd37b884003c ("io_uring/io-wq: don't clear PF_IO_WORKER on exit") Reported-by: Zorro Lang Signed-off-by: Jens Axboe --- io_uring/io-wq.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index fe38eb0cbc82..399e9a15c38d 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -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);