Fix race condition

src/api/s3_copy.rs

@@ -41,45 +41,64 @@ pub async fn handle_copy(
 	};
 
 	let new_uuid = gen_uuid();
+	let new_timestamp = now_msec();
 	let dest_object_version = ObjectVersion {
 		uuid: new_uuid,
-		timestamp: now_msec(),
+		timestamp: new_timestamp,
 		state: ObjectVersionState::Complete(source_last_state.clone()),
 	};
+	let dest_object = Object::new(
+		dest_bucket.to_string(),
+		dest_key.to_string(),
+		vec![dest_object_version],
+	);
 
-	match &source_last_state {
+	match source_last_state {
 		ObjectVersionData::DeleteMarker => {
 			return Err(Error::NotFound);
 		}
 		ObjectVersionData::Inline(_meta, _bytes) => {
-			let dest_object = Object::new(
-				dest_bucket.to_string(),
-				dest_key.to_string(),
-				vec![dest_object_version],
-			);
 			garage.object_table.insert(&dest_object).await?;
 		}
-		ObjectVersionData::FirstBlock(_meta, _first_block_hash) => {
+		ObjectVersionData::FirstBlock(meta, _first_block_hash) => {
+			// Get block list from source version
 			let source_version = garage
 				.version_table
 				.get(&source_last_v.uuid, &EmptyKey)
 				.await?;
 			let source_version = source_version.ok_or(Error::NotFound)?;
 
+			// Write an "uploading" marker in Object table
+			// This holds a reference to the object in the Version table
+			// so that it won't be deleted, e.g. by repair_versions.
+			let tmp_dest_object_version = ObjectVersion {
+				uuid: new_uuid,
+				timestamp: new_timestamp,
+				state: ObjectVersionState::Uploading(meta.headers.clone()),
+			};
+			let tmp_dest_object = Object::new(
+				dest_bucket.to_string(),
+				dest_key.to_string(),
+				vec![tmp_dest_object_version],
+			);
+			garage.object_table.insert(&tmp_dest_object).await?;
+
+			// Write version in the version table. Even with empty block list,
+			// this means that the BlockRef entries linked to this version cannot be
+			// marked as deleted (they are marked as deleted only if the Version
+			// doesn't exist or is marked as deleted).
 			let mut dest_version = Version::new(
 				new_uuid,
 				dest_bucket.to_string(),
 				dest_key.to_string(),
 				false,
 			);
+			garage.version_table.insert(&dest_version).await?;
+
+			// Fill in block list for version and insert block refs
 			for (bk, bv) in source_version.blocks.items().iter() {
 				dest_version.blocks.put(*bk, *bv);
 			}
-			let dest_object = Object::new(
-				dest_bucket.to_string(),
-				dest_key.to_string(),
-				vec![dest_object_version],
-			);
 			let dest_block_refs = dest_version
 				.blocks
 				.items()
@@ -91,14 +110,21 @@ pub async fn handle_copy(
 				})
 				.collect::<Vec<_>>();
 			futures::try_join!(
-				garage.object_table.insert(&dest_object),
 				garage.version_table.insert(&dest_version),
 				garage.block_ref_table.insert_many(&dest_block_refs[..]),
 			)?;
+
+			// Insert final object
+			// We do this last because otherwise there is a race condition in the case where
+			// the copy call has the same source and destination (this happens, rclone does
+			// it to update the modification timestamp for instance). If we did this concurrently
+			// with the stuff before, the block's reference counts could be decremented before
+			// they are incremented again for the new version, leading to data being deleted.
+			garage.object_table.insert(&dest_object).await?;
 		}
 	}
 
-	let now = Utc::now();
+	let now = Utc::now(); // FIXME use the unix timestamp from above
 	let last_modified = now.to_rfc3339_opts(SecondsFormat::Secs, true);
 	let mut xml = String::new();
 	writeln!(&mut xml, r#"<?xml version="1.0" encoding="UTF-8"?>"#).unwrap();

src/api/s3_delete.rs

@@ -29,16 +29,16 @@ async fn handle_delete_internal(
 		_ => true,
 	});
 
-	let mut must_delete = None;
+	let mut version_to_delete = None;
 	let mut timestamp = now_msec();
 	for v in interesting_versions {
-		if v.timestamp + 1 > timestamp || must_delete.is_none() {
-			must_delete = Some(v.uuid);
+		if v.timestamp + 1 > timestamp || version_to_delete.is_none() {
+			version_to_delete = Some(v.uuid);
 		}
 		timestamp = std::cmp::max(timestamp, v.timestamp + 1);
 	}
 
-	let deleted_version = must_delete.ok_or(Error::NotFound)?;
+	let deleted_version = version_to_delete.ok_or(Error::NotFound)?;
 
 	let version_uuid = gen_uuid();
 

src/api/s3_put.rs

@@ -87,17 +87,21 @@ pub async fn handle_put(
 	// that we are uploading something
 	let mut object_version = ObjectVersion {
 		uuid: version_uuid,
-		timestamp: now_msec(),
+		timestamp: version_timestamp,
 		state: ObjectVersionState::Uploading(headers.clone()),
 	};
 	let object = Object::new(bucket.into(), key.into(), vec![object_version.clone()]);
 	garage.object_table.insert(&object).await?;
 
 	// Initialize corresponding entry in version table
+	// Write this entry now, even with empty block list,
+	// to prevent block_ref entries from being deleted (they can be deleted
+	// if the reference a version that isn't found in the version table)
 	let version = Version::new(version_uuid, bucket.into(), key.into(), false);
-	let first_block_hash = blake2sum(&first_block[..]);
+	garage.version_table.insert(&version).await?;
 
 	// Transfer data and verify checksum
+	let first_block_hash = blake2sum(&first_block[..]);
 	let tx_result = read_and_put_blocks(
 		&garage,
 		&version,
@@ -173,7 +177,7 @@ fn ensure_checksum_matches(
 }
 
 async fn read_and_put_blocks(
-	garage: &Arc<Garage>,
+	garage: &Garage,
 	version: &Version,
 	part_number: u64,
 	first_block: Vec<u8>,
@@ -187,7 +191,7 @@ async fn read_and_put_blocks(
 
 	let mut next_offset = first_block.len();
 	let mut put_curr_version_block = put_block_meta(
-		garage.clone(),
+		&garage,
 		&version,
 		part_number,
 		0,
@@ -207,7 +211,7 @@ async fn read_and_put_blocks(
 			let block_hash = blake2sum(&block[..]);
 			let block_len = block.len();
 			put_curr_version_block = put_block_meta(
-				garage.clone(),
+				&garage,
 				&version,
 				part_number,
 				next_offset as u64,
@@ -231,14 +235,13 @@ async fn read_and_put_blocks(
 }
 
 async fn put_block_meta(
-	garage: Arc<Garage>,
+	garage: &Garage,
 	version: &Version,
 	part_number: u64,
 	offset: u64,
 	hash: Hash,
 	size: u64,
 ) -> Result<(), GarageError> {
-	// TODO: don't clone, restart from empty block list ??
 	let mut version = version.clone();
 	version.blocks.put(
 		VersionBlockKey {
@@ -316,6 +319,7 @@ pub async fn handle_create_multipart_upload(
 	let version_uuid = gen_uuid();
 	let headers = get_headers(req)?;
 
+	// Create object in object table
 	let object_version = ObjectVersion {
 		uuid: version_uuid,
 		timestamp: now_msec(),
@@ -324,6 +328,14 @@ pub async fn handle_create_multipart_upload(
 	let object = Object::new(bucket.to_string(), key.to_string(), vec![object_version]);
 	garage.object_table.insert(&object).await?;
 
+	// Insert empty version so that block_ref entries refer to something
+	// (they are inserted concurrently with blocks in the version table, so
+	// there is the possibility that they are inserted before the version table
+	// is created, in which case it is allowed to delete them, e.g. in repair_*)
+	let version = Version::new(version_uuid, bucket.into(), key.into(), false);
+	garage.version_table.insert(&version).await?;
+
+	// Send success response
 	let mut xml = String::new();
 	writeln!(&mut xml, r#"<?xml version="1.0" encoding="UTF-8"?>"#).unwrap();
 	writeln!(
@@ -450,14 +462,12 @@ pub async fn handle_complete_multipart_upload(
 	)?;
 
 	let object = object.ok_or(Error::BadRequest(format!("Object not found")))?;
-	let object_version = object
+	let mut object_version = object
 		.versions()
 		.iter()
-		.find(|v| v.uuid == version_uuid && v.is_uploading());
-	let mut object_version = match object_version {
-		None => return Err(Error::NotFound),
-		Some(x) => x.clone(),
-	};
+		.find(|v| v.uuid == version_uuid && v.is_uploading())
+		.cloned()
+		.ok_or(Error::BadRequest(format!("Version not found")))?;
 
 	let version = version.ok_or(Error::BadRequest(format!("Version not found")))?;
 	if version.blocks.len() == 0 {
@@ -498,12 +508,7 @@ pub async fn handle_complete_multipart_upload(
 	let etag = format!("{}-{}", hex::encode(etag_md5_hasher.finalize()), num_parts);
 
 	// Calculate total size of final object
-	let total_size = version
-		.blocks
-		.items()
-		.iter()
-		.map(|x| x.1.size)
-		.fold(0, |x, y| x + y);
+	let total_size = version.blocks.items().iter().map(|x| x.1.size).sum();
 
 	// Write final object version
 	object_version.state = ObjectVersionState::Complete(ObjectVersionData::FirstBlock(

src/garage/repair.rs

@@ -82,13 +82,7 @@ impl Repair {
 					.versions()
 					.iter()
 					.any(|x| x.uuid == version.uuid && x.state != ObjectVersionState::Aborted),
-				None => {
-					warn!(
-						"Repair versions: object for version {:?} not found, skipping.",
-						version
-					);
-					continue;
-				}
+				None => false,
 			};
 			if !version_exists {
 				info!("Repair versions: marking version as deleted: {:?}", version);
@@ -127,16 +121,8 @@ impl Repair {
 				.version_table
 				.get(&block_ref.version, &EmptyKey)
 				.await?;
-			let ref_exists = match version {
-				Some(v) => !v.deleted.get(),
-				None => {
-					warn!(
-						"Block ref repair: version for block ref {:?} not found, skipping.",
-						block_ref
-					);
-					continue;
-				}
-			};
+			// The version might not exist if it has been GC'ed
+			let ref_exists = version.map(|v| !v.deleted.get()).unwrap_or(false);
 			if !ref_exists {
 				info!(
 					"Repair block ref: marking block_ref as deleted: {:?}",

src/model/block.rs

@@ -28,6 +28,7 @@ use crate::garage::Garage;
 pub const INLINE_THRESHOLD: usize = 3072;
 
 const BLOCK_RW_TIMEOUT: Duration = Duration::from_secs(42);
+const BLOCK_GC_TIMEOUT: Duration = Duration::from_secs(60);
 const NEED_BLOCK_QUERY_TIMEOUT: Duration = Duration::from_secs(5);
 const RESYNC_RETRY_TIMEOUT: Duration = Duration::from_secs(10);
 
@@ -175,7 +176,10 @@ impl BlockManager {
 
 		if data::blake2sum(&data[..]) != *hash {
 			let _lock = self.data_dir_lock.lock().await;
-			warn!("Block {:?} is corrupted. Renaming to .corrupted and resyncing.", hash);
+			warn!(
+				"Block {:?} is corrupted. Renaming to .corrupted and resyncing.",
+				hash
+			);
 			let mut path2 = path.clone();
 			path2.set_extension(".corrupted");
 			fs::rename(path, path2).await?;
@@ -225,7 +229,7 @@ impl BlockManager {
 	pub fn block_decref(&self, hash: &Hash) -> Result<(), Error> {
 		let new_rc = self.rc.merge(&hash, vec![0])?;
 		if new_rc.map(|x| u64_from_bytes(&x[..]) == 0).unwrap_or(true) {
-			self.put_to_resync(&hash, Duration::from_secs(0))?;
+			self.put_to_resync(&hash, BLOCK_GC_TIMEOUT)?;
 		}
 		Ok(())
 	}
@@ -470,7 +474,7 @@ impl BlockManager {
 					};
 					let mut hash = [0u8; 32];
 					hash.copy_from_slice(&hash_bytes[..]);
-					self.put_to_resync(&hash.into(),Duration::from_secs(0))?;
+					self.put_to_resync(&hash.into(), Duration::from_secs(0))?;
 				}
 
 				if *must_exit.borrow() {