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Lock object lifetimes in the lock server are protected by reference counts. References are acquired while holding a lock on an rbtree. Unfortunately, the decision to free lock objects wasn't tested while also holding that lock on the rbtree. A caller putting their object would test the refcount, then wait to get the rbtree lock to remove it from the tree. There's a possible race where the decision is made to remove the object but another reference is added before the object is removed. This was seen in testing and manifest as an incoming request handling path adding a request message to the object before it is freed, losing the message. Clients would then hang on a lock that never saw a response because their request was freed with the lock object. The fix is to hold the rbtree lock when testing the refcount and deciding to free. It adds a bit more contention but not significantly so, given the wild existing contention on a per-fs spinlocked rbtree. Signed-off-by: Zach Brown <zab@versity.com>
Introduction
scoutfs is a clustered in-kernel Linux filesystem designed to support large archival systems. It features additional interfaces and metadata so that archive agents can perform their maintenance workflows without walking all the files in the namespace. Its cluster support lets deployments add nodes to satisfy archival tier bandwidth targets.
The design goal is to reach file populations in the trillions, with the archival bandwidth to match, while remaining operational and responsive.
Highlights of the design and implementation include:
- Fully consistent POSIX semantics between nodes
- Atomic transactions to maintain consistent persistent structures
- Integrated archival metadata replaces syncing to external databases
- Dynamic seperation of resources lets nodes write in parallel
- 64bit throughout; no limits on file or directory sizes or counts
- Open GPLv2 implementation
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