Commit 374117ad authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm mpath: use double checked locking in fast path 



Fast-path code biased toward lazy acknowledgement of bit being set
(primarily only for initialization).  Multipath code is very retry
oriented so even if state is missed it'll recover.

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 564dbb13

drivers/md/dm-mpath.c

+23 −9
Original line number Diff line number Diff line
@@ -128,6 +128,20 @@ static void queue_if_no_path_timeout_work(struct timer_list *t); 
#define MPATHF_PG_INIT_REQUIRED 5		/* pg_init needs calling? */

#define MPATHF_PG_INIT_DELAY_RETRY 6		/* Delay pg_init retry? */



static bool mpath_double_check_test_bit(int MPATHF_bit, struct multipath *m)

{

	bool r = test_bit(MPATHF_bit, &m->flags);



	if (r) {

		unsigned long flags;

		spin_lock_irqsave(&m->lock, flags);

		r = test_bit(MPATHF_bit, &m->flags);

		spin_unlock_irqrestore(&m->lock, flags);

	}



	return r;

}



/*-----------------------------------------------

 * Allocation routines

 *-----------------------------------------------*/
@@ -499,7 +513,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, 


	/* Do we need to select a new pgpath? */

	pgpath = READ_ONCE(m->current_pgpath);

	if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))

	if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))

		pgpath = choose_pgpath(m, nr_bytes);



	if (!pgpath) {
@@ -507,8 +521,8 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, 
			return DM_MAPIO_DELAY_REQUEUE;

		dm_report_EIO(m);	/* Failed */

		return DM_MAPIO_KILL;

	} else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||

		   test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {

	} else if (mpath_double_check_test_bit(MPATHF_QUEUE_IO, m) ||

		   mpath_double_check_test_bit(MPATHF_PG_INIT_REQUIRED, m)) {

		pg_init_all_paths(m);

		return DM_MAPIO_DELAY_REQUEUE;

	}
@@ -598,7 +612,7 @@ static struct pgpath *__map_bio(struct multipath *m, struct bio *bio) 


	/* Do we need to select a new pgpath? */

	pgpath = READ_ONCE(m->current_pgpath);

	if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))

	if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))

		pgpath = choose_pgpath(m, bio->bi_iter.bi_size);



	if (!pgpath) {
@@ -609,8 +623,8 @@ static struct pgpath *__map_bio(struct multipath *m, struct bio *bio) 
		}

		spin_unlock_irqrestore(&m->lock, flags);



	} else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||

		   test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {

	} else if (mpath_double_check_test_bit(MPATHF_QUEUE_IO, m) ||

		   mpath_double_check_test_bit(MPATHF_PG_INIT_REQUIRED, m)) {

		multipath_queue_bio(m, bio);

		pg_init_all_paths(m);

		return ERR_PTR(-EAGAIN);
@@ -861,7 +875,7 @@ static int setup_scsi_dh(struct block_device *bdev, struct multipath *m, 
	struct request_queue *q = bdev_get_queue(bdev);

	int r;



	if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags)) {

	if (mpath_double_check_test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, m)) {

retain:

		if (*attached_handler_name) {

			/*
@@ -1967,11 +1981,11 @@ static int multipath_prepare_ioctl(struct dm_target *ti, 
	int r;



	pgpath = READ_ONCE(m->current_pgpath);

	if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))

	if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))

		pgpath = choose_pgpath(m, 0);



	if (pgpath) {

		if (!test_bit(MPATHF_QUEUE_IO, &m->flags)) {

		if (!mpath_double_check_test_bit(MPATHF_QUEUE_IO, m)) {

			*bdev = pgpath->path.dev->bdev;

			r = 0;

		} else {

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