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Wed, 11 Nov 2026 08:25:06 -0800 (PST) Received: from Tobo ([2605:59c8:3823:2810:e6c7:b59a:50e2:b698]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-860dcb62443sm4799328a34.6.2026.11.11.08.25.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 08:25:06 -0800 (PST) From: Patrick Boake X-Google-Original-From: Patrick Boake Received: from patrick by Tobo with local (Exim 4.96) (envelope-from ) id 1xRB8C-000cy5-2N; Wed, 11 Nov 2026 11:25:04 -0500 To: linux-pm@vger.kernel.org Subject: PM: hibernate freeze/image-creation stage has no watchdog-equivalent protection (real 6h12m stall) Cc: Rafael J. Wysocki X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Message-Id: Date: Wed, 11 Nov 2026 11:25:04 -0500 Hi, Real-world report, not a patch -- happy to help test if useful, but wanted to raise this while it's fresh and while the related watchdog work is active. System: Debian 12.15, kernel 6.1.0-54-amd64 (Debian's packaged LTS -- predates the DPM watchdog extension below, noted explicitly so I'm not overclaiming what I actually reproduced). On 2026-11-10, an automated maintenance script called `systemctl hibernate` after a normal, successful run. Kernel log: Nov 10 03:40:23 kernel: PM: hibernation: hibernation entry Nov 11 09:52:27 kernel: PM: hibernation: Marking nosave pages: ... Nov 11 09:52:28 kernel: PM: hibernation: Creating image: Nov 11 09:52:28 kernel: PM: hibernation: Need to copy 1573875 pages Nov 11 09:52:28 kernel: PM: hibernation: Basic memory bitmaps freed Nov 11 09:52:28 kernel: PM: hibernation: hibernation exit No second "hibernation entry" -- this is one continuous call that took 6h12m to get from entry to its own snapshot-prep steps, then aborted without ever writing an image or powering off. Userspace was frozen for the entire span (a 5-minute heartbeat process went completely silent for the same window), so whatever it was stuck on, it wasn't something a userspace watchdog could have caught -- the watchdog would freeze too. Two things point at where the kernel's own protection stops: 1. Task-freezing has a real, enforced 20s timeout -- a failure there logs "Freezing of tasks failed after 20.0x seconds". That message never appears, which rules out that specific stage. 2. Device suspend/resume has the DPM watchdog. I checked its current scope directly against commit 3339234 ("PM: sleep: Add DPM watchdog to prepare/late/early/noirq/complete phases", landed 2026-09-25) -- it wraps device_prepare, device_suspend_late, device_suspend_noirq, device_resume_noirq, device_resume_early, device_complete. That's the suspend/resume path. It doesn't appear to touch the hibernate-specific freeze/image-creation callback path (the stage our real stall actually hung in, based on where the log picks back up). So: a real stall landed in exactly the stage that (as far as I can tell from the commit itself) still has no watchdog-equivalent coverage, even after the recent extension. I don't have a fix to offer -- this isn't a patch submission -- but given 3339234 is recent and the scope question is fresh, wanted to flag the gap with real evidence rather than file it as a cold, unsubstantiated report. Happy to provide more logs, test a patch, or file this properly via bugzilla.kernel.org instead if that's the better venue for something at this stage (report vs. patch) -- let me know which you'd prefer. Thanks, Patrick Boake patrick@boake.ca