io_uring: move struct io_kiocb from task_struct to io_uring_task

Rather than store the task_struct itself in struct io_kiocb, store
the io_uring specific task_struct. The life times are the same in terms
of io_uring, and this avoids doing some dereferences through the
task_struct. For the hot path of putting local task references, we can
deref req->tctx instead, which we'll need anyway in that function
regardless of whether it's local or remote references.

This is mostly straight forward, except the original task PF_EXITING
check needs a bit of tweaking. task_work is _always_ run from the
originating task, except in the fallback case, where it's run from a
kernel thread. Replace the potentially racy (in case of fallback work)
checks for req->task->flags with current->flags. It's either the still
the original task, in which case PF_EXITING will be sane, or it has
PF_KTHREAD set, in which case it's fallback work. Both cases should
prevent moving forward with the given request.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 15 insertions, 19 deletions

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 43afd9da7d07..7c1ca36b117b 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -206,7 +206,7 @@ bool io_match_task_safe(struct io_kiocb *head, struct io_uring_task *tctx,
 {
 	bool matched;
 
-	if (tctx && head->task->io_uring != tctx)
+	if (tctx && head->tctx != tctx)
 		return false;
 	if (cancel_all)
 		return true;
@@ -407,11 +407,8 @@ static void io_clean_op(struct io_kiocb *req)
 		kfree(req->apoll);
 		req->apoll = NULL;
 	}
-	if (req->flags & REQ_F_INFLIGHT) {
-		struct io_uring_task *tctx = req->task->io_uring;
-
-		atomic_dec(&tctx->inflight_tracked);
-	}
+	if (req->flags & REQ_F_INFLIGHT)
+		atomic_dec(&req->tctx->inflight_tracked);
 	if (req->flags & REQ_F_CREDS)
 		put_cred(req->creds);
 	if (req->flags & REQ_F_ASYNC_DATA) {
@@ -425,7 +422,7 @@ static inline void io_req_track_inflight(struct io_kiocb *req)
 {
 	if (!(req->flags & REQ_F_INFLIGHT)) {
 		req->flags |= REQ_F_INFLIGHT;
-		atomic_inc(&req->task->io_uring->inflight_tracked);
+		atomic_inc(&req->tctx->inflight_tracked);
 	}
 }
 
@@ -514,7 +511,7 @@ static void io_prep_async_link(struct io_kiocb *req)
 static void io_queue_iowq(struct io_kiocb *req)
 {
 	struct io_kiocb *link = io_prep_linked_timeout(req);
-	struct io_uring_task *tctx = req->task->io_uring;
+	struct io_uring_task *tctx = req->tctx;
 
 	BUG_ON(!tctx);
 	BUG_ON(!tctx->io_wq);
@@ -529,7 +526,7 @@ static void io_queue_iowq(struct io_kiocb *req)
 	 * procedure rather than attempt to run this request (or create a new
 	 * worker for it).
 	 */
-	if (WARN_ON_ONCE(!same_thread_group(req->task, current)))
+	if (WARN_ON_ONCE(!same_thread_group(tctx->task, current)))
 		atomic_or(IO_WQ_WORK_CANCEL, &req->work.flags);
 
 	trace_io_uring_queue_async_work(req, io_wq_is_hashed(&req->work));
@@ -678,17 +675,17 @@ static void io_cqring_do_overflow_flush(struct io_ring_ctx *ctx)
 }
 
 /* must to be called somewhat shortly after putting a request */
-static inline void io_put_task(struct task_struct *task)
+static inline void io_put_task(struct io_kiocb *req)
 {
-	struct io_uring_task *tctx = task->io_uring;
+	struct io_uring_task *tctx = req->tctx;
 
-	if (likely(task == current)) {
+	if (likely(tctx->task == current)) {
 		tctx->cached_refs++;
 	} else {
 		percpu_counter_sub(&tctx->inflight, 1);
 		if (unlikely(atomic_read(&tctx->in_cancel)))
 			wake_up(&tctx->wait);
-		put_task_struct(task);
+		put_task_struct(tctx->task);
 	}
 }
 
@@ -1207,7 +1204,7 @@ static inline void io_req_local_work_add(struct io_kiocb *req,
 
 static void io_req_normal_work_add(struct io_kiocb *req)
 {
-	struct io_uring_task *tctx = req->task->io_uring;
+	struct io_uring_task *tctx = req->tctx;
 	struct io_ring_ctx *ctx = req->ctx;
 
 	/* task_work already pending, we're done */
@@ -1226,7 +1223,7 @@ static void io_req_normal_work_add(struct io_kiocb *req)
 		return;
 	}
 
-	if (likely(!task_work_add(req->task, &tctx->task_work, ctx->notify_method)))
+	if (likely(!task_work_add(tctx->task, &tctx->task_work, ctx->notify_method)))
 		return;
 
 	io_fallback_tw(tctx, false);
@@ -1343,8 +1340,7 @@ static void io_req_task_cancel(struct io_kiocb *req, struct io_tw_state *ts)
 void io_req_task_submit(struct io_kiocb *req, struct io_tw_state *ts)
 {
 	io_tw_lock(req->ctx, ts);
-	/* req->task == current here, checking PF_EXITING is safe */
-	if (unlikely(req->task->flags & PF_EXITING))
+	if (unlikely(io_should_terminate_tw()))
 		io_req_defer_failed(req, -EFAULT);
 	else if (req->flags & REQ_F_FORCE_ASYNC)
 		io_queue_iowq(req);
@@ -1403,7 +1399,7 @@ static void io_free_batch_list(struct io_ring_ctx *ctx,
 		}
 		io_put_file(req);
 		io_req_put_rsrc_nodes(req);
-		io_put_task(req->task);
+		io_put_task(req);
 
 		node = req->comp_list.next;
 		io_req_add_to_cache(req, ctx);
@@ -2019,7 +2015,7 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	req->flags = (__force io_req_flags_t) sqe_flags;
 	req->cqe.user_data = READ_ONCE(sqe->user_data);
 	req->file = NULL;
-	req->task = current;
+	req->tctx = current->io_uring;
 	req->cancel_seq_set = false;
 
 	if (unlikely(opcode >= IORING_OP_LAST)) {