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, 13 insertions, 0 deletions

diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 17ffdb1e41c5..702c8e987430 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -426,6 +426,19 @@ static inline bool io_allowed_run_tw(struct io_ring_ctx *ctx)
 		      ctx->submitter_task == current);
 }
 
+/*
+ * Terminate the request if either of these conditions are true:
+ *
+ * 1) It's being executed by the original task, but that task is marked
+ *    with PF_EXITING as it's exiting.
+ * 2) PF_KTHREAD is set, in which case the invoker of the task_work is
+ *    our fallback task_work.
+ */
+static inline bool io_should_terminate_tw(void)
+{
+	return current->flags & (PF_KTHREAD | PF_EXITING);
+}
+
 static inline void io_req_queue_tw_complete(struct io_kiocb *req, s32 res)
 {
 	io_req_set_res(req, res, 0);