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Thu, 11 Dec 2025 03:30:12 +0000 From: Aaron Tomlin To: akpm@linux-foundation.org, lance.yang@linux.dev, mhiramat@kernel.org, gregkh@linuxfoundation.org, pmladek@suse.com Cc: sean@ashe.io, linux-kernel@vger.kernel.org Subject: [PATCH v2 1/2] hung_task: Consolidate hung task warning into an atomic log block Date: Wed, 10 Dec 2025 22:30:03 -0500 Message-ID: <20251211033004.1628875-2-atomlin@atomlin.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251211033004.1628875-1-atomlin@atomlin.com> References: <20251211033004.1628875-1-atomlin@atomlin.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BN9PR03CA0643.namprd03.prod.outlook.com (2603:10b6:408:13b::18) To CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:70::10) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CWLP123MB3523:EE_|CWLP123MB3569:EE_ X-MS-Office365-Filtering-Correlation-Id: 1edb70a3-597f-4041-0058-08de386597c7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014; 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charset="utf-8" Consolidate the multi-line console output in check_hung_task() into a new helper function, hung_task_diagnostics(). This patch ensures the entire diagnostic block (task info, kernel version, and sysctl advice) is logged to the ring buffer via a single pr_err() call. This is critical in a concurrent environment to prevent message lines from interleaving with other CPU activity, thus maintaining contextual integrity of the warning message. Signed-off-by: Aaron Tomlin --- kernel/hung_task.c | 39 +++++++++++++++++++++++++++++---------- 1 file changed, 29 insertions(+), 10 deletions(-) diff --git a/kernel/hung_task.c b/kernel/hung_task.c index d2254c91450b..6f3fb26378b5 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -223,6 +223,34 @@ static inline void debug_show_blocker(struct task_stru= ct *task, unsigned long ti } #endif =20 +/** + * hung_task_diagnostics - Print structured diagnostic info for a hung tas= k. + * @t: The struct task_struct of the detected hung task. + * + * This function consolidates the printing of core diagnostic information + * for a task found to be blocked. This approach ensures atomic logging + * of the multi-line message block, preventing interleaving by other + * console activity, thus maintaining contextual clarity. + */ +static inline void hung_task_diagnostics(struct task_struct *t) +{ + unsigned long blocked_secs =3D (jiffies - t->last_switch_time) / HZ; + const char *coredump_msg =3D ""; + const char *disable_msg =3D + "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" + " disables this message.\n"; + + if (t->flags & PF_POSTCOREDUMP) + coredump_msg =3D " Blocked by coredump.\n"; + + pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n" + " %s %s %.*s\n%s%s", + t->comm, t->pid, blocked_secs, + print_tainted(), init_utsname()->release, + (int)strcspn(init_utsname()->version, " "), + init_utsname()->version, coredump_msg, disable_msg); +} + static void check_hung_task(struct task_struct *t, unsigned long timeout, unsigned long prev_detect_count) { @@ -252,16 +280,7 @@ static void check_hung_task(struct task_struct *t, uns= igned long timeout, if (sysctl_hung_task_warnings || hung_task_call_panic) { if (sysctl_hung_task_warnings > 0) sysctl_hung_task_warnings--; 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charset="utf-8" Introduce support for writing to /proc/sys/kernel/hung_task_detect_count. Writing any value to this file atomically resets the counter of detected hung tasks to zero. This grants system administrators the ability to clear the cumulative diagnostic history after resolving an incident, simplifying monitoring without requiring a system restart. Signed-off-by: Aaron Tomlin --- Documentation/admin-guide/sysctl/kernel.rst | 2 +- kernel/hung_task.c | 30 +++++++++++++++++++-- 2 files changed, 29 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/ad= min-guide/sysctl/kernel.rst index 239da22c4e28..43c17b919969 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -418,7 +418,7 @@ hung_task_detect_count =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 Indicates the total number of tasks that have been detected as hung since -the system boot. +the system boot. The counter can be reset to zero when written to. =20 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled. =20 diff --git a/kernel/hung_task.c b/kernel/hung_task.c index 6f3fb26378b5..979b7e2fcc19 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -377,6 +377,32 @@ static long hung_timeout_jiffies(unsigned long last_ch= ecked, } =20 #ifdef CONFIG_SYSCTL + +/** + * proc_dohung_task_detect_count - proc handler for hung_task_detect_count + * + * Handles read access for the hung task counter. For write access, it + * accepts any successfully parsed value and atomically resets the counter + * to zero. Returns the byte count written on success or a negative error + * code on failure. + */ +static int proc_dohung_task_detect_count(const struct ctl_table *table, in= t write, + void *buffer, size_t *lenp, loff_t *ppos) +{ + int ret; + + if (!write) + return proc_doulongvec_minmax(table, write, buffer, lenp, ppos); + + ret =3D proc_doulongvec_minmax(table, write, buffer, lenp, ppos); + if (ret) + return ret; + + WRITE_ONCE(sysctl_hung_task_detect_count, 0); + + return ret; +} + /* * Process updating of timeout sysctl */ @@ -459,8 +485,8 @@ static const struct ctl_table hung_task_sysctls[] =3D { .procname =3D "hung_task_detect_count", .data =3D &sysctl_hung_task_detect_count, .maxlen =3D sizeof(unsigned long), - .mode =3D 0444, - .proc_handler =3D proc_doulongvec_minmax, + .mode =3D 0644, + .proc_handler =3D proc_dohung_task_detect_count, }, { .procname =3D "hung_task_sys_info", --=20 2.51.0