From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [212.224.123.68]) by lore.proxmox.com (Postfix) with ESMTPS id 638EA1FF15C for ; Fri, 14 Nov 2025 14:18:50 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 7B7A013455; Fri, 14 Nov 2025 14:19:35 +0100 (CET) From: Christian Ebner To: pbs-devel@lists.proxmox.com Date: Fri, 14 Nov 2025 14:18:59 +0100 Message-ID: <20251114131901.441650-20-c.ebner@proxmox.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251114131901.441650-1-c.ebner@proxmox.com> References: <20251114131901.441650-1-c.ebner@proxmox.com> MIME-Version: 1.0 X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1763126341521 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.048 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Subject: [pbs-devel] [PATCH proxmox-backup v6 19/21] datastore: document s3 backend specific locking restrictions X-BeenThere: pbs-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox Backup Server development discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Proxmox Backup Server development discussion Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: pbs-devel-bounces@lists.proxmox.com Sender: "pbs-devel" The requirements are stricter here, since not only must it be avoided to hold std::sync::Mutex guards for async contexts, but also there must be consistency between s3 object store, local datastore cache and in-memory LRU cache. Signed-off-by: Christian Ebner --- pbs-datastore/src/lib.rs | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/pbs-datastore/src/lib.rs b/pbs-datastore/src/lib.rs index 849078a8f..1f7c54ae8 100644 --- a/pbs-datastore/src/lib.rs +++ b/pbs-datastore/src/lib.rs @@ -81,6 +81,19 @@ //! because running these operations concurrently is treated as a feature //! on its own. //! +//! For datastores with S3 backend there are further restrictions since +//! there are 3 types of locking mechanisms involved: +//! - per-chunk file lock +//! - chunk store mutex lock +//! - lru cache mutex lock +//! +//! Locks must always be acquired in this specific order to avoid deadlocks. +//! The per-chunk file lock is used to avoid holding a mutex lock during calls +//! into async contexts, which can deadlock otherwise. It must be held for the +//! whole time from starting an operation on the chunk until it is persisted +//! to s3 backend, local datastore cache and in-memory LRU cache where +//! required. +//! //! ## Inter-process Locking //! //! We need to be able to restart the proxmox-backup service daemons, so -- 2.47.3 _______________________________________________ pbs-devel mailing list pbs-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pbs-devel