From 374117ad4736c5a4f8012cfe59fc07d9d58191d5 Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Mon, 15 Jun 2020 11:31:04 -0400 Subject: 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: Mike Snitzer --- drivers/md/dm-mpath.c | 32 +++++++++++++++++++++++--------- 1 file changed, 23 insertions(+), 9 deletions(-) (limited to 'drivers/md/dm-mpath.c') diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c index f71bb4e5eaf7..88dc7b41b1c6 100644 --- a/drivers/md/dm-mpath.c +++ b/drivers/md/dm-mpath.c @@ -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 { -- cgit