Commit bfe12557 authored by Caleb Sander Mateos's avatar Caleb Sander Mateos Committed by Jens Axboe
Browse files

ublk: optimize ublk_user_copy() on daemon task 



ublk user copy syscalls may be issued from any task, so they take a
reference count on the struct ublk_io to check whether it is owned by
the ublk server and prevent a concurrent UBLK_IO_COMMIT_AND_FETCH_REQ
from completing the request. However, if the user copy syscall is issued
on the io's daemon task, a concurrent UBLK_IO_COMMIT_AND_FETCH_REQ isn't
possible, so the atomic reference count dance is unnecessary. Check for
UBLK_IO_FLAG_OWNED_BY_SRV to ensure the request is dispatched to the
sever and obtain the request from ublk_io's req field instead of looking
it up on the tagset. Skip the reference count increment and decrement.
Commit 8a8fe42d ("ublk: optimize UBLK_IO_REGISTER_IO_BUF on daemon
task") made an analogous optimization for ublk zero copy buffer
registration.

Signed-off-by: default avatarCaleb Sander Mateos <csander@purestorage.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b2503e93

drivers/block/ublk_drv.c

+18 −5
Original line number Diff line number Diff line
@@ -183,7 +183,7 @@ struct ublk_io { 
	 * if user copy or zero copy are enabled:

	 * - UBLK_REFCOUNT_INIT from dispatch to the server

	 *   until UBLK_IO_COMMIT_AND_FETCH_REQ

	 * - 1 for each inflight ublk_ch_{read,write}_iter() call

	 * - 1 for each inflight ublk_ch_{read,write}_iter() call not on task

	 * - 1 for each io_uring registered buffer not registered on task

	 * The I/O can only be completed once all references are dropped.

	 * User copy and buffer registration operations are only permitted
@@ -2698,6 +2698,7 @@ ublk_user_copy(struct kiocb *iocb, struct iov_iter *iter, int dir) 
	struct ublk_io *io;

	unsigned data_len;

	bool is_integrity;

	bool on_daemon;

	size_t buf_off;

	u16 tag, q_id;

	ssize_t ret;
@@ -2727,9 +2728,20 @@ ublk_user_copy(struct kiocb *iocb, struct iov_iter *iter, int dir) 
		return -EINVAL;



	io = &ubq->ios[tag];

	on_daemon = current == READ_ONCE(io->task);

	if (on_daemon) {

		/* On daemon, io can't be completed concurrently, so skip ref */

		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))

			return -EINVAL;



		req = io->req;

		if (!ublk_rq_has_data(req))

			return -EINVAL;

	} else {

		req = __ublk_check_and_get_req(ub, q_id, tag, io);

		if (!req)

			return -EINVAL;

	}



	if (is_integrity) {

		struct blk_integrity *bi = &req->q->limits.integrity;
@@ -2754,6 +2766,7 @@ ublk_user_copy(struct kiocb *iocb, struct iov_iter *iter, int dir) 
		ret = ublk_copy_user_pages(req, buf_off, iter, dir);



out:

	if (!on_daemon)

		ublk_put_req_ref(io, req);

	return ret;

}