This is a note to let you know that I've just added the patch titled io-wq: check for wq exit after adding new worker task_work to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: io-wq-check-for-wq-exit-after-adding-new-worker-task_work.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 71a85387546e50b1a37b0fa45dadcae3bfb35cf6 Mon Sep 17 00:00:00 2001 From: Jens Axboe <axboe@xxxxxxxxx> Date: Fri, 10 Dec 2021 08:29:30 -0700 Subject: io-wq: check for wq exit after adding new worker task_work From: Jens Axboe <axboe@xxxxxxxxx> commit 71a85387546e50b1a37b0fa45dadcae3bfb35cf6 upstream. 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. Reported-and-tested-by: syzbot+b60c982cb0efc5e05a47@xxxxxxxxxxxxxxxxxxxxxxxxx Reviewed-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/io-wq.c | 31 +++++++++++++++++++++++++------ 1 file changed, 25 insertions(+), 6 deletions(-) --- a/fs/io-wq.c +++ b/fs/io-wq.c @@ -141,6 +141,7 @@ static bool io_acct_cancel_pending_work( struct io_wqe_acct *acct, struct io_cb_cancel_data *match); static void create_worker_cb(struct callback_head *cb); +static void io_wq_cancel_tw_create(struct io_wq *wq); static bool io_worker_get(struct io_worker *worker) { @@ -357,10 +358,22 @@ static bool io_queue_worker_create(struc test_and_set_bit_lock(0, &worker->create_state)) goto fail_release; + atomic_inc(&wq->worker_refs); init_task_work(&worker->create_work, func); worker->create_index = acct->index; - if (!task_work_add(wq->task, &worker->create_work, TWA_SIGNAL)) + if (!task_work_add(wq->task, &worker->create_work, TWA_SIGNAL)) { + /* + * EXIT may have been set after checking it above, check after + * adding the task_work and remove any creation item if it is + * now set. wq exit does that too, but we can have added this + * work item after we canceled in io_wq_exit_workers(). + */ + if (test_bit(IO_WQ_BIT_EXIT, &wq->state)) + io_wq_cancel_tw_create(wq); + io_worker_ref_put(wq); return true; + } + io_worker_ref_put(wq); clear_bit_unlock(0, &worker->create_state); fail_release: io_worker_release(worker); @@ -1193,13 +1206,9 @@ void io_wq_exit_start(struct io_wq *wq) set_bit(IO_WQ_BIT_EXIT, &wq->state); } -static void io_wq_exit_workers(struct io_wq *wq) +static void io_wq_cancel_tw_create(struct io_wq *wq) { struct callback_head *cb; - int node; - - if (!wq->task) - return; while ((cb = task_work_cancel_match(wq->task, io_task_work_match, wq)) != NULL) { struct io_worker *worker; @@ -1207,6 +1216,16 @@ static void io_wq_exit_workers(struct io worker = container_of(cb, struct io_worker, create_work); io_worker_cancel_cb(worker); } +} + +static void io_wq_exit_workers(struct io_wq *wq) +{ + int node; + + if (!wq->task) + return; + + io_wq_cancel_tw_create(wq); rcu_read_lock(); for_each_node(node) { Patches currently in stable-queue which might be from axboe@xxxxxxxxx are queue-5.15/iocost-fix-divide-by-zero-on-donation-from-low-hweight-cgroup.patch queue-5.15/io-wq-check-for-wq-exit-after-adding-new-worker-task_work.patch queue-5.15/io-wq-remove-spurious-bit-clear-on-task_work-addition.patch