[PATCH 4/6] io_uring: set task_work notify method at init time

Jens Axboe
2022-04-26T01:49:17Z

While doing so, switch SQPOLL to TWA_SIGNAL_NO_IPI as well, as that
just does a task wakeup and then we can remove the special wakeup we
have in task_work_add.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/io_uring.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 511b52e4b9fd..7e9ac5fd3a8c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -367,6 +367,7 @@ struct io_ring_ctx {

struct io_rings *rings;
unsigned int flags;
+ enum task_work_notify_mode notify_method;
unsigned int compat: 1;
unsigned int drain_next: 1;
unsigned int restricted: 1;
@@ -2651,8 +2652,8 @@ static void tctx_task_work(struct callback_head *cb)
static void io_req_task_work_add(struct io_kiocb *req, bool priority)
{
struct task_struct *tsk = req->task;
+ struct io_ring_ctx *ctx = req->ctx;
struct io_uring_task *tctx = tsk->io_uring;
- enum task_work_notify_mode notify;
struct io_wq_work_node *node;
unsigned long flags;
bool running;
@@ -2675,18 +2676,8 @@ static void io_req_task_work_add(struct io_kiocb *req, bool priority)
if (running)
return;

- /*
- * SQPOLL kernel thread doesn't need notification, just a wakeup. For
- * all other cases, use TWA_SIGNAL unconditionally to ensure we're
- * processing task_work. There's no reliable way to tell if TWA_RESUME
- * will do the job.
- */
- notify = (req->ctx->flags & IORING_SETUP_SQPOLL) ? TWA_NONE : TWA_SIGNAL;
- if (likely(!task_work_add(tsk, &tctx->task_work, notify))) {
- if (notify == TWA_NONE)
- wake_up_process(tsk);
+ if (likely(!task_work_add(tsk, &tctx->task_work, ctx->notify_method)))
return;
- }

spin_lock_irqsave(&tctx->task_lock, flags);
tctx->task_running = false;
@@ -11704,6 +11695,14 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
if (!capable(CAP_IPC_LOCK))
ctx->user = get_uid(current_user());

+ /*
+ * For SQPOLL, we just need a wakeup, always.
+ */
+ if (ctx->flags & IORING_SETUP_SQPOLL)
+ ctx->notify_method = TWA_SIGNAL_NO_IPI;
+ else
+ ctx->notify_method = TWA_SIGNAL;
+
/*
* This is just grabbed for accounting purposes. When a process exits,
* the mm is exited and dropped before the files, hence we need to hang
--
2.35.1