linux-kernel - [v4 PATCH 0/2] hung_task: Provide runtime reset interface for hung task detector

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Message-ID: <20251222014210.2032214-1-atomlin@atomlin.com>
Date: Sun, 21 Dec 2025 20:42:08 -0500
From: Aaron Tomlin <atomlin@...mlin.com>
To: akpm@...ux-foundation.org,
	lance.yang@...ux.dev,
	mhiramat@...nel.org,
	gregkh@...uxfoundation.org,
	pmladek@...e.com,
	joel.granados@...nel.org
Cc: sean@...e.io,
	linux-kernel@...r.kernel.org
Subject: [v4 PATCH 0/2] hung_task: Provide runtime reset interface for hung task detector

Hi Lance, Greg, Petr, Joel,

This series introduces the ability to reset
/proc/sys/kernel/hung_task_detect_count.

Writing a zero value to this file atomically resets the counter of detected
hung tasks. This functionality provides system administrators with the
means to clear the cumulative diagnostic history following incident
resolution, thereby simplifying subsequent monitoring without necessitating
a system restart.

The implementation uses atomic acquire/release semantics to ensure that
diagnostic metadata published by one CPU is correctly observed by the
monitoring thread on another CPU.

Please let me know your thoughts.


Changes since v3 [1]:
 - Use atomic operations to ensure cross-CPU visibility and prevent an integer underflow
 - Use acquire/release semantics for memory ordering (Petr Mladek)
 - Move quoted string to a single line (Petr Mladek)
 - Remove variables coredump_msg and disable_msg to simplify code (Petr Mladek)
 - Add trailing "\n" to all strings to ensure immediate console flushing (Petr Mladek)
 - Improve the hung task counter documentation (Joel Granados)
 - Reject non-zero writes with -EINVAL (Joel Granados)
 - Translate to the new sysctl API (Petr Mladek)

Changes since v2 [2]:
 - Avoided a needless double update to hung_task_detect_count (Lance Yang)
 - Restored previous use of pr_err() for each message (Greg KH)
 - Provided a complete descriptive comment for the helper

Changes since v1 [3]:

 - Removed write-only sysfs attribute (Lance Yang)
 - Modified procfs hung_task_detect_count instead (Lance Yang)
 - Introduced a custom proc_handler
 - Updated documentation (Lance Yang)
 - Added 'static inline' as a hint to eliminate any function call overhead
 - Removed clutter through encapsulation

[1]: https://lore.kernel.org/all/20251216030036.1822217-1-atomlin@atomlin.com/
[2]: https://lore.kernel.org/lkml/20251211033004.1628875-1-atomlin@atomlin.com/
[3]: https://lore.kernel.org/lkml/20251209041218.1583600-1-atomlin@atomlin.com/

Aaron Tomlin (2):
  hung_task: Introduce helper for hung task warning
  hung_task: Enable runtime reset of hung_task_detect_count

 Documentation/admin-guide/sysctl/kernel.rst |   3 +-
 kernel/hung_task.c                          | 109 ++++++++++++++++----
 2 files changed, 90 insertions(+), 22 deletions(-)

-- 
2.51.0