io_uring: cache async and regular file state for fixed files

We have to dig quite deep to check for particularly whether or not a
file supports a fast-path nonblock attempt. For fixed files, we can do
this lookup once and cache the state instead.

This adds two new bits to track whether we support async read/write
attempt, and lines up the REQ_F_ISREG bit with those two. The file slot
re-uses the last 3 (or 2, for 32-bit) of the file pointer to cache that
state, and then we mask it in when we go and use a fixed file.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -690,7 +690,6 @@ enum {
 	REQ_F_CUR_POS_BIT,
 	REQ_F_NOWAIT_BIT,
 	REQ_F_LINK_TIMEOUT_BIT,
-	REQ_F_ISREG_BIT,
 	REQ_F_NEED_CLEANUP_BIT,
 	REQ_F_POLLED_BIT,
 	REQ_F_BUFFER_SELECTED_BIT,
@@ -698,6 +697,10 @@ enum {
 	REQ_F_LTIMEOUT_ACTIVE_BIT,
 	REQ_F_COMPLETE_INLINE_BIT,
 	REQ_F_REISSUE_BIT,
+	/* keep async read/write and isreg together and in order */
+	REQ_F_ASYNC_READ_BIT,
+	REQ_F_ASYNC_WRITE_BIT,
+	REQ_F_ISREG_BIT,
 
 	/* not a real bit, just to check we're not overflowing the space */
 	__REQ_F_LAST_BIT,
@@ -727,8 +730,6 @@ enum {
 	REQ_F_NOWAIT		= BIT(REQ_F_NOWAIT_BIT),
 	/* has or had linked timeout */
 	REQ_F_LINK_TIMEOUT	= BIT(REQ_F_LINK_TIMEOUT_BIT),
-	/* regular file */
-	REQ_F_ISREG		= BIT(REQ_F_ISREG_BIT),
 	/* needs cleanup */
 	REQ_F_NEED_CLEANUP	= BIT(REQ_F_NEED_CLEANUP_BIT),
 	/* already went through poll handler */
@@ -743,6 +744,12 @@ enum {
 	REQ_F_COMPLETE_INLINE	= BIT(REQ_F_COMPLETE_INLINE_BIT),
 	/* caller should reissue async */
 	REQ_F_REISSUE		= BIT(REQ_F_REISSUE_BIT),
+	/* supports async reads */
+	REQ_F_ASYNC_READ	= BIT(REQ_F_ASYNC_READ_BIT),
+	/* supports async writes */
+	REQ_F_ASYNC_WRITE	= BIT(REQ_F_ASYNC_WRITE_BIT),
+	/* regular file */
+	REQ_F_ISREG		= BIT(REQ_F_ISREG_BIT),
 };
 
 struct async_poll {
@@ -2651,7 +2658,7 @@ static bool io_bdev_nowait(struct block_device *bdev)
  * any file. For now, just ensure that anything potentially problematic is done
  * inline.
  */
-static bool io_file_supports_async(struct file *file, int rw)
+static bool __io_file_supports_async(struct file *file, int rw)
 {
 	umode_t mode = file_inode(file)->i_mode;
 
@@ -2684,6 +2691,16 @@ static bool io_file_supports_async(struct file *file, int rw)
 	return file->f_op->write_iter != NULL;
 }
 
+static bool io_file_supports_async(struct io_kiocb *req, int rw)
+{
+	if (rw == READ && (req->flags & REQ_F_ASYNC_READ))
+		return true;
+	else if (rw == WRITE && (req->flags & REQ_F_ASYNC_WRITE))
+		return true;
+
+	return __io_file_supports_async(req->file, rw);
+}
+
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -2692,7 +2709,7 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	unsigned ioprio;
 	int ret;
 
-	if (S_ISREG(file_inode(file)->i_mode))
+	if (!(req->flags & REQ_F_ISREG) && S_ISREG(file_inode(file)->i_mode))
 		req->flags |= REQ_F_ISREG;
 
 	kiocb->ki_pos = READ_ONCE(sqe->off);
@@ -3289,7 +3306,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 		kiocb->ki_flags |= IOCB_NOWAIT;
 
 	/* If the file doesn't support async, just async punt */
-	if (force_nonblock && !io_file_supports_async(req->file, READ)) {
+	if (force_nonblock && !io_file_supports_async(req, READ)) {
 		ret = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
 		return ret ?: -EAGAIN;
 	}
@@ -3394,7 +3411,7 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		kiocb->ki_flags |= IOCB_NOWAIT;
 
 	/* If the file doesn't support async, just async punt */
-	if (force_nonblock && !io_file_supports_async(req->file, WRITE))
+	if (force_nonblock && !io_file_supports_async(req, WRITE))
 		goto copy_iov;
 
 	/* file path doesn't support NOWAIT for non-direct_IO */
@@ -5173,7 +5190,7 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
 	else
 		return false;
 	/* if we can't nonblock try, then no point in arming a poll handler */
-	if (!io_file_supports_async(req->file, rw))
+	if (!io_file_supports_async(req, rw))
 		return false;
 
 	apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
@@ -6182,6 +6199,15 @@ static void io_wq_submit_work(struct io_wq_work *work)
 	}
 }
 
+#define FFS_ASYNC_READ		0x1UL
+#define FFS_ASYNC_WRITE		0x2UL
+#ifdef CONFIG_64BIT
+#define FFS_ISREG		0x4UL
+#else
+#define FFS_ISREG		0x0UL
+#endif
+#define FFS_MASK		~(FFS_ASYNC_READ|FFS_ASYNC_WRITE|FFS_ISREG)
+
 static inline struct file **io_fixed_file_slot(struct fixed_rsrc_data *file_data,
 					       unsigned i)
 {
@@ -6194,7 +6220,9 @@ static inline struct file **io_fixed_file_slot(struct fixed_rsrc_data *file_data
 static inline struct file *io_file_from_index(struct io_ring_ctx *ctx,
 					      int index)
 {
-	return *io_fixed_file_slot(ctx->file_data, index);
+	struct file **file_slot = io_fixed_file_slot(ctx->file_data, index);
+
+	return (struct file *) ((unsigned long) *file_slot & FFS_MASK);
 }
 
 static struct file *io_file_get(struct io_submit_state *state,
@@ -6204,10 +6232,16 @@ static struct file *io_file_get(struct io_submit_state *state,
 	struct file *file;
 
 	if (fixed) {
+		unsigned long file_ptr;
+
 		if (unlikely((unsigned int)fd >= ctx->nr_user_files))
 			return NULL;
 		fd = array_index_nospec(fd, ctx->nr_user_files);
-		file = io_file_from_index(ctx, fd);
+		file_ptr = (unsigned long) *io_fixed_file_slot(ctx->file_data, fd);
+		file = (struct file *) (file_ptr & FFS_MASK);
+		file_ptr &= ~FFS_MASK;
+		/* mask in overlapping REQ_F and FFS bits */
+		req->flags |= (file_ptr << REQ_F_ASYNC_READ_BIT);
 		io_set_resource_node(req);
 	} else {
 		trace_io_uring_file_get(ctx, fd);
@@ -7556,6 +7590,8 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 		goto out_free;
 
 	for (i = 0; i < nr_args; i++, ctx->nr_user_files++) {
+		unsigned long file_ptr;
+
 		if (copy_from_user(&fd, &fds[i], sizeof(fd))) {
 			ret = -EFAULT;
 			goto out_fput;
@@ -7580,7 +7616,14 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 			fput(file);
 			goto out_fput;
 		}
-		*io_fixed_file_slot(file_data, i) = file;
+		file_ptr = (unsigned long) file;
+		if (__io_file_supports_async(file, READ))
+			file_ptr |= FFS_ASYNC_READ;
+		if (__io_file_supports_async(file, WRITE))
+			file_ptr |= FFS_ASYNC_WRITE;
+		if (S_ISREG(file_inode(file)->i_mode))
+			file_ptr |= FFS_ISREG;
+		*io_fixed_file_slot(file_data, i) = (struct file *) file_ptr;
 	}
 
 	ret = io_sqe_files_scm(ctx);
@@ -7713,7 +7756,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 		file_slot = io_fixed_file_slot(ctx->file_data, i);
 
 		if (*file_slot) {
-			err = io_queue_file_removal(data, *file_slot);
+			file = (struct file *) ((unsigned long) *file_slot & FFS_MASK);
+			err = io_queue_file_removal(data, file);
 			if (err)
 				break;
 			*file_slot = NULL;
@@ -9288,7 +9332,7 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 	seq_printf(m, "SqThreadCpu:\t%d\n", sq ? task_cpu(sq->thread) : -1);
 	seq_printf(m, "UserFiles:\t%u\n", ctx->nr_user_files);
 	for (i = 0; has_lock && i < ctx->nr_user_files; i++) {
-		struct file *f = *io_fixed_file_slot(ctx->file_data, i);
+		struct file *f = io_file_from_index(ctx, i);
 
 		if (f)
 			seq_printf(m, "%5u: %s\n", i, file_dentry(f)->d_iname);