The rw-semaphore is acquired for read only on two places, none of them is performance-critical. So, we can replace it with a mutex.
Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-snap.c | 82 +++++++++++++++++++++++++-------------------------- 1 file changed, 41 insertions(+), 41 deletions(-) Index: linux-2.6/drivers/md/dm-snap.c =================================================================== --- linux-2.6.orig/drivers/md/dm-snap.c +++ linux-2.6/drivers/md/dm-snap.c @@ -47,7 +47,7 @@ struct dm_exception_table { }; struct dm_snapshot { - struct rw_semaphore lock; + struct mutex lock; struct dm_dev *origin; struct dm_dev *cow; @@ -439,9 +439,9 @@ static int __find_snapshots_sharing_cow( 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) @@ -909,7 +909,7 @@ static int remove_single_exception_chunk 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 @@ -924,7 +924,7 @@ static int remove_single_exception_chunk b = __release_queued_bios_after_merge(s); out: - up_write(&s->lock); + mutex_unlock(&s->lock); if (b) flush_bios(b); @@ -983,9 +983,9 @@ static void snapshot_merge_next_chunks(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; } @@ -1026,10 +1026,10 @@ static void snapshot_merge_next_chunks(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++) @@ -1071,10 +1071,10 @@ static void merge_callback(int read_err, 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); @@ -1173,7 +1173,7 @@ static int snapshot_ctr(struct dm_target 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; @@ -1338,9 +1338,9 @@ static void snapshot_dtr(struct dm_targe /* 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); @@ -1458,7 +1458,7 @@ static void pending_complete(void *conte if (!success) { /* Read/write error - snapshot is unusable */ - down_write(&s->lock); + mutex_lock(&s->lock); __invalidate_snapshot(s, -EIO); error = 1; goto out; @@ -1466,14 +1466,14 @@ static void pending_complete(void *conte 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; @@ -1498,7 +1498,7 @@ 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) { @@ -1694,7 +1694,7 @@ static int snapshot_map(struct dm_target /* 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)) { @@ -1717,9 +1717,9 @@ static int snapshot_map(struct dm_target 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); @@ -1754,7 +1754,7 @@ static int snapshot_map(struct dm_target 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; } @@ -1764,7 +1764,7 @@ static int snapshot_map(struct dm_target 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; } @@ -1774,7 +1774,7 @@ static int snapshot_map(struct dm_target } out_unlock: - up_write(&s->lock); + mutex_unlock(&s->lock); out: return r; } @@ -1810,7 +1810,7 @@ static int snapshot_merge_map(struct dm_ 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) @@ -1841,12 +1841,12 @@ 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; } @@ -1878,7 +1878,7 @@ static int snapshot_preresume(struct dm_ 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."); @@ -1888,7 +1888,7 @@ static int snapshot_preresume(struct dm_ "source is suspended."); r = -EINVAL; } - up_read(&snap_src->lock); + mutex_unlock(&snap_src->lock); } up_read(&_origins_lock); @@ -1934,11 +1934,11 @@ static void snapshot_resume(struct dm_ta (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); @@ -1953,9 +1953,9 @@ static void snapshot_resume(struct dm_ta /* 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) @@ -1995,7 +1995,7 @@ static void snapshot_status(struct dm_ta switch (type) { case STATUSTYPE_INFO: - down_write(&snap->lock); + mutex_lock(&snap->lock); if (!snap->valid) DMEMIT("Invalid"); @@ -2020,7 +2020,7 @@ static void snapshot_status(struct dm_ta DMEMIT("Unknown"); } - up_write(&snap->lock); + mutex_unlock(&snap->lock); break; @@ -2086,7 +2086,7 @@ static int __origin_write(struct list_he 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) @@ -2113,9 +2113,9 @@ static int __origin_write(struct list_he 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); @@ -2158,7 +2158,7 @@ static int __origin_write(struct list_he } next_snapshot: - up_write(&snap->lock); + mutex_unlock(&snap->lock); if (pe_to_start_now) { start_copy(pe_to_start_now); -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
