On 19/02/2021 17:09, Jens Axboe wrote:
> We hit this case when the task is exiting, and we need somewhere to
> do background cleanup of requests. Instead of relying on the io-wq
> task manager to do this work for us, just stuff it somewhere where
> we can safely run it ourselves directly.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> fs/io-wq.c | 12 ------------
> fs/io-wq.h | 2 --
> fs/io_uring.c | 38 +++++++++++++++++++++++++++++++++++---
> 3 files changed, 35 insertions(+), 17 deletions(-)
>
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index c36bbcd823ce..800b299f9772 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -16,7 +16,6 @@
> #include <linux/kthread.h>
> #include <linux/rculist_nulls.h>
> #include <linux/fs_struct.h>
> -#include <linux/task_work.h>
> #include <linux/blk-cgroup.h>
> #include <linux/audit.h>
> #include <linux/cpu.h>
> @@ -775,9 +774,6 @@ static int io_wq_manager(void *data)
> complete(&wq->done);
>
> while (!kthread_should_stop()) {
> - if (current->task_works)
> - task_work_run();
> -
> for_each_node(node) {
> struct io_wqe *wqe = wq->wqes[node];
> bool fork_worker[2] = { false, false };
> @@ -800,9 +796,6 @@ static int io_wq_manager(void *data)
> schedule_timeout(HZ);
> }
>
> - if (current->task_works)
> - task_work_run();
> -
> out:
> if (refcount_dec_and_test(&wq->refs)) {
> complete(&wq->done);
> @@ -1160,11 +1153,6 @@ void io_wq_destroy(struct io_wq *wq)
> __io_wq_destroy(wq);
> }
>
> -struct task_struct *io_wq_get_task(struct io_wq *wq)
> -{
> - return wq->manager;
> -}
> -
> static bool io_wq_worker_affinity(struct io_worker *worker, void *data)
> {
> struct task_struct *task = worker->task;
> diff --git a/fs/io-wq.h b/fs/io-wq.h
> index 096f1021018e..a1610702f222 100644
> --- a/fs/io-wq.h
> +++ b/fs/io-wq.h
> @@ -124,8 +124,6 @@ typedef bool (work_cancel_fn)(struct io_wq_work *, void *);
> enum io_wq_cancel io_wq_cancel_cb(struct io_wq *wq, work_cancel_fn *cancel,
> void *data, bool cancel_all);
>
> -struct task_struct *io_wq_get_task(struct io_wq *wq);
> -
> #if defined(CONFIG_IO_WQ)
> extern void io_wq_worker_sleeping(struct task_struct *);
> extern void io_wq_worker_running(struct task_struct *);
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index d951acb95117..bbd1ec7aa9e9 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -455,6 +455,9 @@ struct io_ring_ctx {
>
> struct io_restriction restrictions;
>
> + /* exit task_work */
> + struct callback_head *exit_task_work;
> +
> /* Keep this last, we don't need it for the fast path */
> struct work_struct exit_work;
> };
> @@ -2313,11 +2316,14 @@ static int io_req_task_work_add(struct io_kiocb *req)
> static void io_req_task_work_add_fallback(struct io_kiocb *req,
> task_work_func_t cb)
> {
> - struct task_struct *tsk = io_wq_get_task(req->ctx->io_wq);
> + struct io_ring_ctx *ctx = req->ctx;
> + struct callback_head *head;
>
> init_task_work(&req->task_work, cb);
> - task_work_add(tsk, &req->task_work, TWA_NONE);
> - wake_up_process(tsk);
> + do {
> + head = ctx->exit_task_work;
> + req->task_work.next = head;
> + } while (cmpxchg(&ctx->exit_task_work, head, &req->task_work) != head);
> }
>
> static void __io_req_task_cancel(struct io_kiocb *req, int error)
> @@ -9258,6 +9264,30 @@ void __io_uring_task_cancel(void)
> io_uring_remove_task_files(tctx);
> }
>
> +static void io_run_ctx_fallback(struct io_ring_ctx *ctx)
> +{
> + struct callback_head *work, *head, *next;
> +
> + do {
> + do {
> + head = NULL;
> + work = READ_ONCE(ctx->exit_task_work);
> + if (!work)
> + break;
> + } while (cmpxchg(&ctx->exit_task_work, work, head) != work);
Looking at io_uring-worker.v3, it's actually just xchg() without do-while.
work = xchg(&ctx->exit_task_work, NULL);
> +
> + if (!work)
> + break;
> +
> + do {
> + next = work->next;
> + work->func(work);
> + work = next;
> + cond_resched();
> + } while (work);
> + } while (1);
> +}
> +
> static int io_uring_flush(struct file *file, void *data)
> {
> struct io_uring_task *tctx = current->io_uring;
> @@ -9268,6 +9298,8 @@ static int io_uring_flush(struct file *file, void *data)
> io_req_caches_free(ctx, current);
> }
>
> + io_run_ctx_fallback(ctx);
> +
> if (!tctx)
> return 0;
>
>
--
Pavel Begunkov
