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Commit 2f78d4ba authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Stefan Bader
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dm snapshot: use mutex instead of rw_semaphore 

BugLink: https://bugs.launchpad.net/bugs/1851549

[ Upstream commit ae1093be ]

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarConnor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: default avatarKhalid Elmously <khalid.elmously@canonical.com>
parent 855c328c
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Inline Side-by-side
Showing with 43 additions and 41 deletions
drivers/md/dm-snap.c
View file @ 2f78d4ba
......@@ -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;
......@@ -457,9 +457,9 @@ 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)
......@@ -927,7 +927,7 @@ 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
......@@ -942,7 +942,7 @@ 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);
......@@ -1001,9 +1001,9 @@ 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;
}
......@@ -1044,10 +1044,10 @@ 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++)
......@@ -1089,10 +1089,10 @@ 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);
......@@ -1191,7 +1191,7 @@ 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;
......@@ -1358,9 +1358,9 @@ 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);
......@@ -1391,6 +1391,8 @@ 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);
......@@ -1478,7 +1480,7 @@ 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;
......@@ -1486,14 +1488,14 @@ 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;
......@@ -1520,7 +1522,7 @@ static void pending_complete(void *context, int success)
}
increment_pending_exceptions_done_count();
up_write(&s->lock);
mutex_unlock(&s->lock);
/* Submit any pending write bios */
if (error) {
......@@ -1720,7 +1722,7 @@ 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_rw(bio) == WRITE)) {
r = -EIO;
......@@ -1742,9 +1744,9 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
if (bio_rw(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);
......@@ -1779,7 +1781,7 @@ 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;
}
......@@ -1789,7 +1791,7 @@ 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;
}
......@@ -1799,7 +1801,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
}
out_unlock:
up_write(&s->lock);
mutex_unlock(&s->lock);
out:
return r;
}
......@@ -1835,7 +1837,7 @@ 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)
......@@ -1866,12 +1868,12 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
bio->bi_bdev = s->origin->bdev;
if (bio_rw(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;
}
......@@ -1902,7 +1904,7 @@ 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.");
......@@ -1912,7 +1914,7 @@ 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);
......@@ -1958,11 +1960,11 @@ 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);
......@@ -1977,9 +1979,9 @@ 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)
......@@ -2019,7 +2021,7 @@ 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");
......@@ -2044,7 +2046,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type,
DMEMIT("Unknown");
}
up_write(&snap->lock);
mutex_unlock(&snap->lock);
break;
......@@ -2110,7 +2112,7 @@ 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)
......@@ -2137,9 +2139,9 @@ 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);
......@@ -2182,7 +2184,7 @@ 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);
......
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