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There's a race possible where set_valid_greeting() runs just as
another greeting reply sits on the resend_queue from a handshake:
1. server_greeting() calls scoutfs_net_response() to queue the
server's greeting reply on send_queue and kicks send_work.
2. server_greeting() falls through to scoutfs_net_server_greeting()
which calls set_valid_greeting() under conn->lock.
3. If send_work already ran between steps 1 and 2 it moved the
reply onto resend_queue.
4. set_valid_greeting() splices resend_queue back into send_queue,
re-queueing the greeting reply for a second send on the same
socket.
The receiver treats a duplicate greeting as fatal: the recieve path
invalid_message check on the saw_greeting flag tears the connection
down silently. The client never sees a normal disconnect, just a
stalled connection, and the server only notices once the 30s
recovery timeout fires and fences the client.
Fix by walking resend_queue in set_valid_greeting() and dropping any
queued greeting before splicing them in. Dropping them should be safe
and mimics what scoutfs_net_shutdown_worker() does.
Signed-off-by: Auke Kok <auke.kok@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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