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The d_prune_aliases in lock invalidation was thought to be safe because the caller had an inode refernece, surely it can't get into iput_final. I missed the fundamental dcache pattern that dput can ascend through parents and end up in inode eviction for entirely unrelated inodes. It's very easy for this to deadlock, imagine if nothing else that the inode invalidation is blocked on in dput->iput->evict->delete->lock is itself in the list of locks to invalidate in the caller. We fix this by always kicking off d_prune and dput into async work. This increases the chance that inodes will still be referenced after invalidation and prevent inline deletion. More deletions can be deferred until the orphan scanner finds them. It should be rare, though. We're still likely to put and drop invalidated inodes before a writer gets around to removing the final unlink and asking us for the omap that describes our cached inodes. To perform the d_prune in work we make it a behavioural flag and make our queued iputs a little more robust. We use much safer and understandable locking to cover the count and the new flags and we put the work in re-entrant work in their own workqueue instead of one work instance in the system_wq. 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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