Do signal-aware waits and meta snapshot

[jserv]

dnsfs_query_record no longer re-waits uninterruptibly after a signal wakes wait_for_completion_interruptible. A signaled foreground waiter now returns -ERESTARTSYS at once, drops its reference, and reads no req fields (the worker may still be writing them). Safe by the existing refcount contract: the worker holds its own reference until after complete_all, so the shared coalesced request stays queued, still resolves, fills the cache, and wakes the other waiters; the last reference drop frees it. Adds test_signal_interrupt: a 3s-delayed resolver, SIGINT a cat once the wire query is observed, expect it to die within 1s.

dnsfs_storage_assemble_once and dnsfs_storage_read_range_once snapshot storage->meta and storage->epoch into locals before sizing buffers. The read path runs without storage->lock, so a concurrent re-pin could grow chunk_count or size between the allocation and the loop bound, a heap OOB write; the snapshot closes it. A torn generation is caught by epoch/CRC and retried.

dnsfs_query_tcp loops kernel_sendmsg until the whole framed query is sent (TCP is a byte stream) and fails a zero-length send; dnsfs_query_udp_once requires the datagram send to report the ful length.

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Summary by cubic

Make DNS queries signal-aware and harden send/read paths. Interrupted reads return fast, storage reads snapshot metadata to avoid races, and TCP/UDP sends ensure full writes.

• Bug Fixes
  • dnsfs_query_record: on signal, return -ERESTARTSYS immediately, drop ref, and avoid reading request fields.
  • Snapshot storage->meta and storage->epoch in assemble/read paths to prevent heap OOB during lockless reads; torn generations are retried via epoch/CRC.
  • TCP: loop kernel_sendmsg until the full framed query is sent; treat zero-length send as -EIO. UDP: require full datagram length or fail.
  • Added test_signal_interrupt to verify a SIGINT aborts a slow read within 1s.

^{Written for commit dd43a09. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}