Messages in this thread |  | | From | Mayank Rungta via B4 Relay <> | | Subject | [PATCH 0/4] watchdog/hardlockup: Improvements to hardlockup detection and documentation | | Date | Thu, 12 Feb 2026 14:12:09 -0700 |
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This series addresses limitations in the hardlockup detector implementations and updates the documentation to reflect actual behavior and recent changes.
The changes are structured as follows:
Hardlockup Detection Improvements (Patches 1 & 3) ================================================= The hardlockup detector logic relies on updating saved interrupt counts to determine if the CPU is making progress.
Patch 1 ensures that the saved interrupt count is updated unconditionally before checking the "touched" flag. This prevents stale comparisons which can delay detection. This is a logic fix that ensures the detector remains accurate even when the watchdog is frequently touched.
Patch 3 improves the Buddy detector's timeliness. The current checking interval (every 3rd sample) causes high variability in detection time (up to 24s). This patch changes the Buddy detector to check at every hrtimer interval (4s) with a missed-interrupt threshold of 3, narrowing the detection window to a consistent 8-12 second range.
Documentation Updates (Patches 2 & 4) ===================================== The current documentation does not fully capture the variable nature of detection latency or the details of the Buddy system.
Patch 2 removes the strict "10 seconds" definition of a hardlockup, which was misleading given the periodic nature of the detector. It adds a "Detection Overhead" section to the admin guide, using "Best Case" and "Worst Case" scenarios to illustrate that detection time can vary significantly (e.g., ~6s to ~20s).
Patch 4 adds a dedicated section for the Buddy detector, which was previously undocumented. It details the mechanism, the new timing logic, and known limitations.
Signed-off-by: Mayank Rungta <mrungta@google.com> --- Mayank Rungta (4): watchdog/hardlockup: Always update saved interrupts during check doc: watchdog: Clarify hardlockup detection timing watchdog/hardlockup: improve buddy system detection timeliness doc: watchdog: Document buddy detector
Documentation/admin-guide/lockup-watchdogs.rst | 132 +++++++++++++++++++++---- include/linux/nmi.h | 1 + kernel/watchdog.c | 41 ++++++-- kernel/watchdog_buddy.c | 9 +- 4 files changed, 146 insertions(+), 37 deletions(-) --- base-commit: 0dddf20b4fd4afd59767acc144ad4da60259f21f change-id: 20260211-hardlockup-watchdog-fixes-60317598ac20
Best regards, -- Mayank Rungta <mrungta@google.com>
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