io_uring: extract a helper for ctx quiesce

Refactor __io_uring_register() by extracting a helper responsible for
ctx queisce. Looks better and will make it easier to add more
optimisations.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0339e0027504176be09237eefa7945bf9a6f153d.1628471125.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -10074,6 +10074,33 @@ static bool io_register_op_must_quiesce(int op)
 	}
 }
 
+static int io_ctx_quiesce(struct io_ring_ctx *ctx)
+{
+	long ret;
+
+	percpu_ref_kill(&ctx->refs);
+
+	/*
+	 * Drop uring mutex before waiting for references to exit. If another
+	 * thread is currently inside io_uring_enter() it might need to grab the
+	 * uring_lock to make progress. If we hold it here across the drain
+	 * wait, then we can deadlock. It's safe to drop the mutex here, since
+	 * no new references will come in after we've killed the percpu ref.
+	 */
+	mutex_unlock(&ctx->uring_lock);
+	do {
+		ret = wait_for_completion_interruptible(&ctx->ref_comp);
+		if (!ret)
+			break;
+		ret = io_run_task_work_sig();
+	} while (ret >= 0);
+	mutex_lock(&ctx->uring_lock);
+
+	if (ret)
+		io_refs_resurrect(&ctx->refs, &ctx->ref_comp);
+	return ret;
+}
+
 static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			       void __user *arg, unsigned nr_args)
 	__releases(ctx->uring_lock)
@@ -10098,31 +10125,9 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 	}
 
 	if (io_register_op_must_quiesce(opcode)) {
-		percpu_ref_kill(&ctx->refs);
-
-		/*
-		 * Drop uring mutex before waiting for references to exit. If
-		 * another thread is currently inside io_uring_enter() it might
-		 * need to grab the uring_lock to make progress. If we hold it
-		 * here across the drain wait, then we can deadlock. It's safe
-		 * to drop the mutex here, since no new references will come in
-		 * after we've killed the percpu ref.
-		 */
-		mutex_unlock(&ctx->uring_lock);
-		do {
-			ret = wait_for_completion_interruptible(&ctx->ref_comp);
-			if (!ret)
-				break;
-			ret = io_run_task_work_sig();
-			if (ret < 0)
-				break;
-		} while (1);
-		mutex_lock(&ctx->uring_lock);
-
-		if (ret) {
-			io_refs_resurrect(&ctx->refs, &ctx->ref_comp);
+		ret = io_ctx_quiesce(ctx);
+		if (ret)
 			return ret;
-		}
 	}
 
 	switch (opcode) {