rajamesandClaude Opus 5.5
0dbc98c049
On riscv64 a system=v3 boot never reached its prompt: Artemis's writes
"timed out" and Zuse was never confirmed (logs/20261026-134850). vblk_io()
bounded its wait by ~1M polling iterations, which on riscv64 under TCG is
about one heartbeat tick of real time -- shorter than a write that allocates
space in a sparse host image. Instrumented, the request was seen completing
just after the give-up ("used idx=409 last=408"), and every later request
then took its predecessor's completion for its own and returned before its
own I/O was done (a stale used index at each later request), reusing the
descriptor chain while the device still owned it: silent read and write
corruption from that point on. FABRIC-3.md's 2026-09-09 "request that never
gets a used-ring completion" is this same early give-up.
Now: the wait is for this request's own completion (the used index
reaching the avail index it was given), bounded by 5 s of real time on the
CPU's counter (timer_now_ns(), which needs no interrupts); a request that
truly never completes takes the disk out of service instead of letting a
later request reuse the chain.
Red (riscv64 system=v3, with temporary instrumentation): 151003, 151100 --
a timeout then dozens of stale completions each. Green: 151238, 151332 --
none; Zuse confirmed; the keyboard line answered. system=v3 with the fix:
riscv64 151438, amd64 151528, aarch64 151610, no timeouts. Accepted (v4):
151722, 151916, 152247, POST 538/538, dict_hash 0xfec8c47cfc6f437f;
test-32, 39 modules, 0 failures.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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