From 63c103279a95e82280092f2f4232e91e8117a252 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Thu, 15 Oct 2026 19:30:28 +0000 Subject: [PATCH] io_uring/io-wq: don't lose the signal that ends work When a thread exits, only its tracked requests are cancelled. Then its io-wq is torn down. io_wq_exit_workers() signals every worker, to get it out of an interruptible sleep, and waits for all of them to exit. Before they do, they go through the work that is left. Unbounded work is cancelled. Bounded work is run, as it is expected to end by itself. Not all of it does. An open has no file yet, so it counts as bounded, and the open of a FIFO waits for the other end. That is what the signal is for. But the workers are signalled once, and a worker that hasn't started the work by then loses the signal: io_wq_exit_workers() io_worker_handle_work() io_wq_worker_wake() set TIF_NOTIFY_SIGNAL io_assign_current_work() io_run_task_work() clear TIF_NOTIFY_SIGNAL io_wq_submit_work() fifo_open() wait_for_partner() wait_for_completion_timeout() The thread never gets out of do_exit(): IORING_OP_OPENAT of a FIFO without a writer, IOSQE_ASYNC exit of the thread that has submitted it hangs in more than 9 of 10 attempts (4 CPUs, KVM), until the process is killed. Set TIF_NOTIFY_SIGNAL for bounded work that is started with IO_WQ_BIT_EXIT set. The bit is set before the workers are signalled, and it is tested after the flag has been cleared, with clear_notify_signal() providing the barrier. So either the flag stays, or the bit is seen. Work that is started while the io-wq exits is treated like work that is being run at that time: it isn't interrupted unless it waits interruptibly. Fixes: afcc4015d1bf ("io-wq: provide an io_wq_put_and_exit() helper") Assisted-by: LLM Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-4-c1556f5d7bf5@toxicpanda.com Signed-off-by: Jens Axboe --- io_uring/io-wq.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index 97523ccc7a71..433c003a83e5 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -655,9 +655,15 @@ static void io_worker_handle_work(struct io_wq_acct *acct, next_hashed = wq_next_work(work); - if (do_kill && - (work_flags & IO_WQ_WORK_UNBOUND)) + /* + * io_wq_exit_workers() signals us once, so that we + * don't sleep for ever. If that was before this work + * became the current one, the signal is gone. + */ + if (do_kill && (work_flags & IO_WQ_WORK_UNBOUND)) atomic_or(IO_WQ_WORK_CANCEL, &work->flags); + else if (do_kill) + set_notify_signal(current); req = container_of(work, struct io_kiocb, work); kcov_remote_start_common(req->ctx->kcov_handle); io_wq_submit_work(work);