[PATCH 4.14 02/95] dm snapshot: use mutex instead of rw_semaphore

From: Mikulas Patocka mpatocka@redhat.com

[ Upstream commit ae1093be5a0ef997833e200a0dafb9ed0b1ff4fe ]

The rw_semaphore is acquired for read only in two places, neither is performance-critical. So replace it with a mutex -- which is more efficient.

Signed-off-by: Mikulas Patocka mpatocka@redhat.com Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/dm-snap.c | 84 +++++++++++++++++++++++--------------------- 1 file changed, 43 insertions(+), 41 deletions(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index b502debc6df3f..8b1556e77a0a0 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -48,7 +48,7 @@ struct dm_exception_table { };

struct dm_snapshot { - struct rw_semaphore lock; + struct mutex lock;

struct dm_dev *origin; struct dm_dev *cow; @@ -456,9 +456,9 @@ static int __find_snapshots_sharing_cow(struct dm_snapshot *snap, if (!bdev_equal(s->cow->bdev, snap->cow->bdev)) continue;

- down_read(&s->lock); + mutex_lock(&s->lock); active = s->active; - up_read(&s->lock); + mutex_unlock(&s->lock);

if (active) { if (snap_src) @@ -926,7 +926,7 @@ static int remove_single_exception_chunk(struct dm_snapshot *s) int r; chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;

- down_write(&s->lock); + mutex_lock(&s->lock);

/* * Process chunks (and associated exceptions) in reverse order @@ -941,7 +941,7 @@ static int remove_single_exception_chunk(struct dm_snapshot *s) b = __release_queued_bios_after_merge(s);

out: - up_write(&s->lock); + mutex_unlock(&s->lock); if (b) flush_bios(b);

@@ -1000,9 +1000,9 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s) if (linear_chunks < 0) { DMERR("Read error in exception store: " "shutting down merge"); - down_write(&s->lock); + mutex_lock(&s->lock); s->merge_failed = 1; - up_write(&s->lock); + mutex_unlock(&s->lock); } goto shut; } @@ -1043,10 +1043,10 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s) previous_count = read_pending_exceptions_done_count(); }

- down_write(&s->lock); + mutex_lock(&s->lock); s->first_merging_chunk = old_chunk; s->num_merging_chunks = linear_chunks; - up_write(&s->lock); + mutex_unlock(&s->lock);

/* Wait until writes to all 'linear_chunks' drain */ for (i = 0; i < linear_chunks; i++) @@ -1088,10 +1088,10 @@ static void merge_callback(int read_err, unsigned long write_err, void *context) return;

shut: - down_write(&s->lock); + mutex_lock(&s->lock); s->merge_failed = 1; b = __release_queued_bios_after_merge(s); - up_write(&s->lock); + mutex_unlock(&s->lock); error_bios(b);

merge_shutdown(s); @@ -1190,7 +1190,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv) s->exception_start_sequence = 0; s->exception_complete_sequence = 0; INIT_LIST_HEAD(&s->out_of_order_list); - init_rwsem(&s->lock); + mutex_init(&s->lock); INIT_LIST_HEAD(&s->list); spin_lock_init(&s->pe_lock); s->state_bits = 0; @@ -1357,9 +1357,9 @@ static void snapshot_dtr(struct dm_target *ti) /* Check whether exception handover must be cancelled */ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest && (s == snap_src)) { - down_write(&snap_dest->lock); + mutex_lock(&snap_dest->lock); snap_dest->valid = 0; - up_write(&snap_dest->lock); + mutex_unlock(&snap_dest->lock); DMERR("Cancelling snapshot handover."); } up_read(&_origins_lock); @@ -1390,6 +1390,8 @@ static void snapshot_dtr(struct dm_target *ti)

dm_exception_store_destroy(s->store);

+ mutex_destroy(&s->lock); + dm_put_device(ti, s->cow);

dm_put_device(ti, s->origin); @@ -1477,7 +1479,7 @@ static void pending_complete(void *context, int success)

if (!success) { /* Read/write error - snapshot is unusable */ - down_write(&s->lock); + mutex_lock(&s->lock); __invalidate_snapshot(s, -EIO); error = 1; goto out; @@ -1485,14 +1487,14 @@ static void pending_complete(void *context, int success)

e = alloc_completed_exception(GFP_NOIO); if (!e) { - down_write(&s->lock); + mutex_lock(&s->lock); __invalidate_snapshot(s, -ENOMEM); error = 1; goto out; } *e = pe->e;

- down_write(&s->lock); + mutex_lock(&s->lock); if (!s->valid) { free_completed_exception(e); error = 1; @@ -1517,7 +1519,7 @@ out: full_bio->bi_end_io = pe->full_bio_end_io; increment_pending_exceptions_done_count();

- up_write(&s->lock); + mutex_unlock(&s->lock);

/* Submit any pending write bios */ if (error) { @@ -1716,7 +1718,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)

/* FIXME: should only take write lock if we need * to copy an exception */ - down_write(&s->lock); + mutex_lock(&s->lock);

if (!s->valid || (unlikely(s->snapshot_overflowed) && bio_data_dir(bio) == WRITE)) { @@ -1739,9 +1741,9 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) if (bio_data_dir(bio) == WRITE) { pe = __lookup_pending_exception(s, chunk); if (!pe) { - up_write(&s->lock); + mutex_unlock(&s->lock); pe = alloc_pending_exception(s); - down_write(&s->lock); + mutex_lock(&s->lock);

if (!s->valid || s->snapshot_overflowed) { free_pending_exception(pe); @@ -1776,7 +1778,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) bio->bi_iter.bi_size == (s->store->chunk_size << SECTOR_SHIFT)) { pe->started = 1; - up_write(&s->lock); + mutex_unlock(&s->lock); start_full_bio(pe, bio); goto out; } @@ -1786,7 +1788,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) if (!pe->started) { /* this is protected by snap->lock */ pe->started = 1; - up_write(&s->lock); + mutex_unlock(&s->lock); start_copy(pe); goto out; } @@ -1796,7 +1798,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) }

out_unlock: - up_write(&s->lock); + mutex_unlock(&s->lock); out: return r; } @@ -1832,7 +1834,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)

chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);

- down_write(&s->lock); + mutex_lock(&s->lock);

/* Full merging snapshots are redirected to the origin */ if (!s->valid) @@ -1863,12 +1865,12 @@ redirect_to_origin: bio_set_dev(bio, s->origin->bdev);

if (bio_data_dir(bio) == WRITE) { - up_write(&s->lock); + mutex_unlock(&s->lock); return do_origin(s->origin, bio); }

out_unlock: - up_write(&s->lock); + mutex_unlock(&s->lock);

return r; } @@ -1900,7 +1902,7 @@ static int snapshot_preresume(struct dm_target *ti) down_read(&_origins_lock); (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) { - down_read(&snap_src->lock); + mutex_lock(&snap_src->lock); if (s == snap_src) { DMERR("Unable to resume snapshot source until " "handover completes."); @@ -1910,7 +1912,7 @@ static int snapshot_preresume(struct dm_target *ti) "source is suspended."); r = -EINVAL; } - up_read(&snap_src->lock); + mutex_unlock(&snap_src->lock); } up_read(&_origins_lock);

@@ -1956,11 +1958,11 @@ static void snapshot_resume(struct dm_target *ti)

(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) { - down_write(&snap_src->lock); - down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING); + mutex_lock(&snap_src->lock); + mutex_lock_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING); __handover_exceptions(snap_src, snap_dest); - up_write(&snap_dest->lock); - up_write(&snap_src->lock); + mutex_unlock(&snap_dest->lock); + mutex_unlock(&snap_src->lock); }

up_read(&_origins_lock); @@ -1975,9 +1977,9 @@ static void snapshot_resume(struct dm_target *ti) /* Now we have correct chunk size, reregister */ reregister_snapshot(s);

- down_write(&s->lock); + mutex_lock(&s->lock); s->active = 1; - up_write(&s->lock); + mutex_unlock(&s->lock); }

static uint32_t get_origin_minimum_chunksize(struct block_device *bdev) @@ -2017,7 +2019,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type, switch (type) { case STATUSTYPE_INFO:

- down_write(&snap->lock); + mutex_lock(&snap->lock);

if (!snap->valid) DMEMIT("Invalid"); @@ -2042,7 +2044,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type, DMEMIT("Unknown"); }

- up_write(&snap->lock); + mutex_unlock(&snap->lock);

break;

@@ -2108,7 +2110,7 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, if (dm_target_is_snapshot_merge(snap->ti)) continue;

- down_write(&snap->lock); + mutex_lock(&snap->lock);

/* Only deal with valid and active snapshots */ if (!snap->valid || !snap->active) @@ -2135,9 +2137,9 @@ static int __origin_write(struct list_head *snapshots, sector_t sector,

pe = __lookup_pending_exception(snap, chunk); if (!pe) { - up_write(&snap->lock); + mutex_unlock(&snap->lock); pe = alloc_pending_exception(snap); - down_write(&snap->lock); + mutex_lock(&snap->lock);

if (!snap->valid) { free_pending_exception(pe); @@ -2180,7 +2182,7 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, }

next_snapshot: - up_write(&snap->lock); + mutex_unlock(&snap->lock);

if (pe_to_start_now) { start_copy(pe_to_start_now);