io_uring: assign new io_identity for task if members have changed

This avoids doing a copy for each new async IO, if some parts of the
io_identity has changed. We avoid reference counting for the normal
fast path of nothing ever changing.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1066,12 +1066,18 @@ static void io_init_identity(struct io_identity *id)
  */
 static inline void io_req_init_async(struct io_kiocb *req)
 {
+	struct io_uring_task *tctx = current->io_uring;
+
 	if (req->flags & REQ_F_WORK_INITIALIZED)
 		return;
 
 	memset(&req->work, 0, sizeof(req->work));
 	req->flags |= REQ_F_WORK_INITIALIZED;
-	req->work.identity = &current->io_uring->identity;
+
+	/* Grab a ref if this isn't our static identity */
+	req->work.identity = tctx->identity;
+	if (tctx->identity != &tctx->__identity)
+		refcount_inc(&req->work.identity->count);
 }
 
 static inline bool io_async_submit(struct io_ring_ctx *ctx)
@@ -1179,7 +1185,7 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
 
 static void io_put_identity(struct io_uring_task *tctx, struct io_kiocb *req)
 {
-	if (req->work.identity == &tctx->identity)
+	if (req->work.identity == &tctx->__identity)
 		return;
 	if (refcount_dec_and_test(&req->work.identity->count))
 		kfree(req->work.identity);
@@ -1254,11 +1260,12 @@ static bool io_identity_cow(struct io_kiocb *req)
 	refcount_inc(&id->count);
 
 	/* drop old identity, assign new one. one ref for req, one for tctx */
-	if (req->work.identity != &tctx->identity &&
+	if (req->work.identity != tctx->identity &&
 	    refcount_sub_and_test(2, &req->work.identity->count))
 		kfree(req->work.identity);
 
 	req->work.identity = id;
+	tctx->identity = id;
 	return true;
 }
 
@@ -7691,7 +7698,8 @@ static int io_uring_alloc_task_context(struct task_struct *task)
 	tctx->in_idle = 0;
 	atomic_long_set(&tctx->req_issue, 0);
 	atomic_long_set(&tctx->req_complete, 0);
-	io_init_identity(&tctx->identity);
+	io_init_identity(&tctx->__identity);
+	tctx->identity = &tctx->__identity;
 	task->io_uring = tctx;
 	return 0;
 }
@@ -7701,6 +7709,9 @@ void __io_uring_free(struct task_struct *tsk)
 	struct io_uring_task *tctx = tsk->io_uring;
 
 	WARN_ON_ONCE(!xa_empty(&tctx->xa));
+	WARN_ON_ONCE(refcount_read(&tctx->identity->count) != 1);
+	if (tctx->identity != &tctx->__identity)
+		kfree(tctx->identity);
 	kfree(tctx);
 	tsk->io_uring = NULL;
 }

include/linux/io_uring.h

@@ -24,7 +24,8 @@ struct io_uring_task {
 	struct wait_queue_head	wait;
 	struct file		*last;
 	atomic_long_t		req_issue;
-	struct io_identity	identity;
+	struct io_identity	__identity;
+	struct io_identity	*identity;
 
 	/* completion side */
 	bool			in_idle ____cacheline_aligned_in_smp;