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dm mpath: use double checked locking in fast path

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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 <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer 2020-06-15 11:31:04 -04:00
parent 564dbb130b
commit 374117ad47
1 changed files with 23 additions and 9 deletions
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32
drivers/md/dm-mpath.c
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@ -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 {