linux-kernel - Re: [PATCH] hung_task: add warning counter to blocked task report

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Message-ID: <582cf973-1290-493c-b821-f23480e75014@linux.dev>
Date: Mon, 21 Jul 2025 13:45:31 +0800
From: Ye Liu <ye.liu@...ux.dev>
To: Lance Yang <lance.yang@...ux.dev>
Cc: Ye Liu <liuye@...inos.cn>, linux-kernel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Zi Li <zi.li@...ux.dev>
Subject: Re: [PATCH] hung_task: add warning counter to blocked task report



On 2025/7/21 12:56, Lance Yang wrote:
> Hi Ye,
> 
> Thanks for your patch!
> 
> On 2025/7/21 11:17, Ye Liu wrote:
>> From: Ye Liu <liuye@...inos.cn>
>>
>> Add a warning counter to each hung task message to make it easier
>> to analyze and locate issues in the logs.
>>
>> Signed-off-by: Ye Liu <liuye@...inos.cn>
>> ---
>>   kernel/hung_task.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
>> index 8708a1205f82..9e5f86148d47 100644
>> --- a/kernel/hung_task.c
>> +++ b/kernel/hung_task.c
>> @@ -58,6 +58,7 @@ EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
>>   static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
>>     static int __read_mostly sysctl_hung_task_warnings = 10;
>> +static int hung_task_warning_count;
>>     static int __read_mostly did_panic;
>>   static bool hung_task_show_lock;
>> @@ -232,8 +233,9 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>>       if (sysctl_hung_task_warnings || hung_task_call_panic) {
>>           if (sysctl_hung_task_warnings > 0)
>>               sysctl_hung_task_warnings--;
>> -        pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
>> -               t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
>> +        pr_err("INFO: task %s:%d blocked for more than %ld seconds. [Warning #%d]\n",
>> +               t->comm, t->pid, (jiffies - t->last_switch_time) / HZ,
>> +               ++hung_task_warning_count);
>>           pr_err("      %s %s %.*s\n",
>>               print_tainted(), init_utsname()->release,
>>               (int)strcspn(init_utsname()->version, " "),
> 
> A quick thought on this: we already have the hung_task_detect_count
> counter, which tracks the total number of hung tasks detected since
> boot ;)
> 
> While this patch adds a counter inline with the warning message, the
> existing counter already provides a way to know how many hung task
> events have occurred.
> 
> Could you elaborate on the specific benefit of printing this count
> directly in the log, compared to checking the global hung_task_detect_count?
> 
> Also, if the goal is to give each warning a unique sequence number,
> I think the dmesg timestamp prefix serves the same purpose ;)
> 
> Thanks,
> Lance

Sorry for not noticing sysctl_hung_task_detect_count. 
I just thought adding it directly to the warning message would make the 
log easier to read and more intuitive than relying on timestamps.                            

If accepted, I will send V2, like this:

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 8708a1205f82..231afdb68bb2 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -232,8 +232,9 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
        if (sysctl_hung_task_warnings || hung_task_call_panic) {
                if (sysctl_hung_task_warnings > 0)
                        sysctl_hung_task_warnings--;
-               pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
-                      t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
+               pr_err("INFO: task %s:%d blocked for more than %ld seconds. [#%ld]\n",
+                      t->comm, t->pid, (jiffies - t->last_switch_time) / HZ,
+                      sysctl_hung_task_detect_count);
                pr_err("      %s %s %.*s\n",
                        print_tainted(), init_utsname()->release,
                        (int)strcspn(init_utsname()->version, " "),