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https://github.com/versity/versitygw.git
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Carl MercierandClaude Fable 5
f7e13d71ce
S3 conditional writes (If-Match / If-None-Match: *) were evaluated with a check-then-act pattern: PutObjectWithPostFunc and CompleteMultipartUploadWithCopy read the current etag, evaluated the precondition, and only later published the replacement via link/rename. Under concurrent conditional PUTs to the same key, many writers could read the same old state, all pass the check, and all succeed, breaking compare-and-swap coordination built on conditional writes (observed by Buzz's git object-store A3 conformance probe: 32-way races returned up to 32 winners instead of exactly 1x2xx + 31x412). Introduce a per-object publish lock (lockObjectPublish) that every object publication path holds across condition re-evaluation, metadata stores, and the final link: - Exclusion is an advisory file lock (flock on unix, LockFileEx on windows) on bucket/.sgwtmp/objlock/<shard>, where shard is the first byte of sha256(key). The gateway is stateless and multiple gateway processes may share one filesystem, so a process-local mutex alone is not sufficient; file locks provide cross-process and (via NFSv4 lock semantics) cross-client exclusion. A process-local striped mutex is taken alongside so in-process contention never thrashes the filesystem lock. Lock files are empty, bounded (max 256 per bucket), and never unlinked to avoid the unlink/recreate flock race that cannot be detected reliably on NFS. - Request bodies are staged to the temp file before the lock is taken; the lock covers only the short commit phase. The kernel releases the lock on close or process death, so failures and crashes cannot leave a stale lock. If the filesystem does not support advisory locking (e.g. NFS mounted with -o nolock), the gateway falls back to process-local exclusion and warns once. - The pre-staging precondition check is kept as an advisory fast-fail; the authoritative check runs under the lock. Unconditional PUTs, directory-object PUTs, CopyObject (via PutObject), scoutfs (via PutObjectWithPostFunc/CompleteMultipartUploadWithCopy), and multipart completion all participate. - For conditional writes on versioned buckets the version snapshot is deferred until the precondition is confirmed under the lock, so losing writers no longer create spurious version snapshots. - The postprocess hook now runs before any path-based metadata is written, so a failing hook no longer leaves stale sidecar attributes (previously the new etag was visible in sidecar mode even when publication failed). Add regression tests covering 32-way If-Match and If-None-Match: * races for both ordinary PUT and multipart completion, mixed conditional/unconditional races, sequential semantics, per-key independence, and cleanup after failed publication, for both xattr and sidecar metadata modes. Add an external SigV4 test (tests/conditionalrace) that replicates the Buzz A3 probe against a live gateway, optionally across two gateway processes sharing one backend directory. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
53 lines
1.4 KiB
Go
53 lines
1.4 KiB
Go
// Copyright 2026 Versity Software
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// This file is licensed under the Apache License, Version 2.0
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// (the "License"); you may not use this file except in compliance
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// with the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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//go:build windows
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package posix
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import (
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"context"
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"errors"
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"os"
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"time"
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"golang.org/x/sys/windows"
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)
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// lockFileExclusive takes an exclusive lock on f via LockFileEx, polling with
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// backoff so that context cancellation is honored while waiting. The lock is
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// released when f is closed or the process exits.
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func lockFileExclusive(ctx context.Context, f *os.File) error {
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backoff := objLockInitialBackoff
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for {
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ol := new(windows.Overlapped)
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err := windows.LockFileEx(windows.Handle(f.Fd()),
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windows.LOCKFILE_EXCLUSIVE_LOCK|windows.LOCKFILE_FAIL_IMMEDIATELY,
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0, 1, 0, ol)
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if err == nil {
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return nil
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}
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if !errors.Is(err, windows.ERROR_LOCK_VIOLATION) {
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return err
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}
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select {
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case <-ctx.Done():
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return ctx.Err()
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case <-time.After(backoff):
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}
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backoff = min(backoff*2, objLockMaxBackoff)
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}
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}
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