io_uring/uring_cmd: avoid double indirect call in task work dispatch

io_uring task work dispatch makes an indirect call to struct io_kiocb's
io_task_work.func field to allow running arbitrary task work functions.
In the uring_cmd case, this calls io_uring_cmd_work(), which immediately
makes another indirect call to struct io_uring_cmd's task_work_cb field.
Change the uring_cmd task work callbacks to functions whose signatures
match io_req_tw_func_t. Add a function io_uring_cmd_from_tw() to convert
from the task work's struct io_tw_req argument to struct io_uring_cmd *.
Define a constant IO_URING_CMD_TASK_WORK_ISSUE_FLAGS to avoid
manufacturing issue_flags in the uring_cmd task work callbacks. Now
uring_cmd task work dispatch makes a single indirect call to the
uring_cmd implementation's callback. This also allows removing the
task_work_cb field from struct io_uring_cmd, freeing up 8 bytes for
future storage.
Since fuse_uring_send_in_task() now has access to the io_tw_token_t,
check its cancel field directly instead of relying on the
IO_URING_F_TASK_DEAD issue flag.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 13 insertions, 9 deletions

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 7509025b4071..375fd048c4cb 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -11,17 +11,13 @@
 /* io_uring_cmd is being issued again */
 #define IORING_URING_CMD_REISSUE	(1U << 31)
 
-typedef void (*io_uring_cmd_tw_t)(struct io_uring_cmd *cmd,
-				  unsigned issue_flags);
-
 struct io_uring_cmd {
 	struct file	*file;
 	const struct io_uring_sqe *sqe;
-	/* callback to defer completions to task context */
-	io_uring_cmd_tw_t task_work_cb;
 	u32		cmd_op;
 	u32		flags;
 	u8		pdu[32]; /* available inline for free use */
+	u8		unused[8];
 };
 
 static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
@@ -60,7 +56,7 @@ void __io_uring_cmd_done(struct io_uring_cmd *cmd, s32 ret, u64 res2,
 			 unsigned issue_flags, bool is_cqe32);
 
 void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
-			    io_uring_cmd_tw_t task_work_cb,
+			    io_req_tw_func_t task_work_cb,
 			    unsigned flags);
 
 /*
@@ -109,7 +105,7 @@ static inline void __io_uring_cmd_done(struct io_uring_cmd *cmd, s32 ret,
 {
 }
 static inline void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
-			    io_uring_cmd_tw_t task_work_cb, unsigned flags)
+			    io_req_tw_func_t task_work_cb, unsigned flags)
 {
 }
 static inline void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
@@ -132,15 +128,23 @@ static inline bool io_uring_mshot_cmd_post_cqe(struct io_uring_cmd *ioucmd,
 }
 #endif
 
+static inline struct io_uring_cmd *io_uring_cmd_from_tw(struct io_tw_req tw_req)
+{
+	return io_kiocb_to_cmd(tw_req.req, struct io_uring_cmd);
+}
+
+/* task_work executor checks the deferred list completion */
+#define IO_URING_CMD_TASK_WORK_ISSUE_FLAGS IO_URING_F_COMPLETE_DEFER
+
 /* users must follow the IOU_F_TWQ_LAZY_WAKE semantics */
 static inline void io_uring_cmd_do_in_task_lazy(struct io_uring_cmd *ioucmd,
-			io_uring_cmd_tw_t task_work_cb)
+			io_req_tw_func_t task_work_cb)
 {
 	__io_uring_cmd_do_in_task(ioucmd, task_work_cb, IOU_F_TWQ_LAZY_WAKE);
 }
 
 static inline void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
-			io_uring_cmd_tw_t task_work_cb)
+			io_req_tw_func_t task_work_cb)
 {
 	__io_uring_cmd_do_in_task(ioucmd, task_work_cb, 0);
 }