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dm mpath: use atomic_t for counting members of 'struct multipath'
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The use of atomic_t for nr_valid_paths, pg_init_in_progress and
pg_init_count will allow relaxing the use of the m->lock spinlock.

Suggested-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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Mike Snitzer committed May 5, 2016
1 parent 518257b commit 91e968a
Showing 1 changed file with 33 additions and 28 deletions.
61 changes: 33 additions & 28 deletions drivers/md/dm-mpath.c
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Original file line number Diff line number Diff line change
Expand Up @@ -76,19 +76,19 @@ struct multipath {

wait_queue_head_t pg_init_wait; /* Wait for pg_init completion */

unsigned pg_init_in_progress; /* Only one pg_init allowed at once */

unsigned nr_valid_paths; /* Total number of usable paths */
struct pgpath *current_pgpath;
struct priority_group *current_pg;
struct priority_group *next_pg; /* Switch to this PG if set */

unsigned long flags; /* Multipath state flags */

unsigned pg_init_retries; /* Number of times to retry pg_init */
unsigned pg_init_count; /* Number of times pg_init called */
unsigned pg_init_delay_msecs; /* Number of msecs before pg_init retry */

atomic_t nr_valid_paths; /* Total number of usable paths */
atomic_t pg_init_in_progress; /* Only one pg_init allowed at once */
atomic_t pg_init_count; /* Number of times pg_init called */

struct work_struct trigger_event;

/*
Expand Down Expand Up @@ -195,6 +195,9 @@ static struct multipath *alloc_multipath(struct dm_target *ti, bool use_blk_mq)
INIT_LIST_HEAD(&m->priority_groups);
spin_lock_init(&m->lock);
set_bit(MPATHF_QUEUE_IO, &m->flags);
atomic_set(&m->nr_valid_paths, 0);
atomic_set(&m->pg_init_in_progress, 0);
atomic_set(&m->pg_init_count, 0);
m->pg_init_delay_msecs = DM_PG_INIT_DELAY_DEFAULT;
INIT_WORK(&m->trigger_event, trigger_event);
init_waitqueue_head(&m->pg_init_wait);
Expand Down Expand Up @@ -279,10 +282,10 @@ static int __pg_init_all_paths(struct multipath *m)
struct pgpath *pgpath;
unsigned long pg_init_delay = 0;

if (m->pg_init_in_progress || test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
if (atomic_read(&m->pg_init_in_progress) || test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
return 0;

m->pg_init_count++;
atomic_inc(&m->pg_init_count);
clear_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);

/* Check here to reset pg_init_required */
Expand All @@ -298,9 +301,9 @@ static int __pg_init_all_paths(struct multipath *m)
continue;
if (queue_delayed_work(kmpath_handlerd, &pgpath->activate_path,
pg_init_delay))
m->pg_init_in_progress++;
atomic_inc(&m->pg_init_in_progress);
}
return m->pg_init_in_progress;
return atomic_read(&m->pg_init_in_progress);
}

static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
Expand All @@ -316,7 +319,7 @@ static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
clear_bit(MPATHF_QUEUE_IO, &m->flags);
}

m->pg_init_count = 0;
atomic_set(&m->pg_init_count, 0);
}

static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg,
Expand All @@ -341,7 +344,7 @@ static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
struct priority_group *pg;
bool bypassed = true;

if (!m->nr_valid_paths) {
if (!atomic_read(&m->nr_valid_paths)) {
clear_bit(MPATHF_QUEUE_IO, &m->flags);
goto failed;
}
Expand Down Expand Up @@ -902,14 +905,17 @@ static int multipath_ctr(struct dm_target *ti, unsigned int argc,
/* parse the priority groups */
while (as.argc) {
struct priority_group *pg;
unsigned nr_valid_paths = atomic_read(&m->nr_valid_paths);

pg = parse_priority_group(&as, m);
if (IS_ERR(pg)) {
r = PTR_ERR(pg);
goto bad;
}

m->nr_valid_paths += pg->nr_pgpaths;
nr_valid_paths += pg->nr_pgpaths;
atomic_set(&m->nr_valid_paths, nr_valid_paths);

list_add_tail(&pg->list, &m->priority_groups);
pg_count++;
pg->pg_num = pg_count;
Expand Down Expand Up @@ -939,19 +945,14 @@ static int multipath_ctr(struct dm_target *ti, unsigned int argc,
static void multipath_wait_for_pg_init_completion(struct multipath *m)
{
DECLARE_WAITQUEUE(wait, current);
unsigned long flags;

add_wait_queue(&m->pg_init_wait, &wait);

while (1) {
set_current_state(TASK_UNINTERRUPTIBLE);

spin_lock_irqsave(&m->lock, flags);
if (!m->pg_init_in_progress) {
spin_unlock_irqrestore(&m->lock, flags);
if (!atomic_read(&m->pg_init_in_progress))
break;
}
spin_unlock_irqrestore(&m->lock, flags);

io_schedule();
}
Expand Down Expand Up @@ -1001,13 +1002,13 @@ static int fail_path(struct pgpath *pgpath)
pgpath->is_active = false;
pgpath->fail_count++;

m->nr_valid_paths--;
atomic_dec(&m->nr_valid_paths);

if (pgpath == m->current_pgpath)
m->current_pgpath = NULL;

dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
pgpath->path.dev->name, m->nr_valid_paths);
pgpath->path.dev->name, atomic_read(&m->nr_valid_paths));

schedule_work(&m->trigger_event);

Expand All @@ -1025,6 +1026,7 @@ static int reinstate_path(struct pgpath *pgpath)
int r = 0, run_queue = 0;
unsigned long flags;
struct multipath *m = pgpath->pg->m;
unsigned nr_valid_paths;

spin_lock_irqsave(&m->lock, flags);

Expand All @@ -1039,16 +1041,17 @@ static int reinstate_path(struct pgpath *pgpath)

pgpath->is_active = true;

if (!m->nr_valid_paths++) {
nr_valid_paths = atomic_inc_return(&m->nr_valid_paths);
if (nr_valid_paths == 1) {
m->current_pgpath = NULL;
run_queue = 1;
} else if (m->hw_handler_name && (m->current_pg == pgpath->pg)) {
if (queue_work(kmpath_handlerd, &pgpath->activate_path.work))
m->pg_init_in_progress++;
atomic_inc(&m->pg_init_in_progress);
}

dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
pgpath->path.dev->name, m->nr_valid_paths);
pgpath->path.dev->name, nr_valid_paths);

schedule_work(&m->trigger_event);

Expand Down Expand Up @@ -1166,7 +1169,8 @@ static bool pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)

spin_lock_irqsave(&m->lock, flags);

if (m->pg_init_count <= m->pg_init_retries && !test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
if (atomic_read(&m->pg_init_count) <= m->pg_init_retries &&
!test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
set_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);
else
limit_reached = true;
Expand Down Expand Up @@ -1236,7 +1240,7 @@ static void pg_init_done(void *data, int errors)
} else if (!test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags))
pg->bypassed = false;

if (--m->pg_init_in_progress)
if (atomic_dec_return(&m->pg_init_in_progress) > 0)
/* Activations of other paths are still on going */
goto out;

Expand Down Expand Up @@ -1317,7 +1321,7 @@ static int do_end_io(struct multipath *m, struct request *clone,
fail_path(mpio->pgpath);

spin_lock_irqsave(&m->lock, flags);
if (!m->nr_valid_paths) {
if (!atomic_read(&m->nr_valid_paths)) {
if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
if (!__must_push_back(m))
r = -EIO;
Expand Down Expand Up @@ -1421,7 +1425,8 @@ static void multipath_status(struct dm_target *ti, status_type_t type,

/* Features */
if (type == STATUSTYPE_INFO)
DMEMIT("2 %u %u ", test_bit(MPATHF_QUEUE_IO, &m->flags), m->pg_init_count);
DMEMIT("2 %u %u ", test_bit(MPATHF_QUEUE_IO, &m->flags),
atomic_read(&m->pg_init_count));
else {
DMEMIT("%u ", test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) +
(m->pg_init_retries > 0) * 2 +
Expand Down Expand Up @@ -1675,8 +1680,8 @@ static int multipath_busy(struct dm_target *ti)
spin_lock_irqsave(&m->lock, flags);

/* pg_init in progress or no paths available */
if (m->pg_init_in_progress ||
(!m->nr_valid_paths && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))) {
if (atomic_read(&m->pg_init_in_progress) ||
(!atomic_read(&m->nr_valid_paths) && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))) {
busy = true;
goto out;
}
Expand Down

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