Re: [PATCH v2] hung_task: Add per-round stack trace deduplication

[kernel test robot <lkp@intel.com>]

Hi Aaron,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v7.2-rc7 next-20260813]
[cannot apply to linux-review/Aaron-Tomlin/hung_task-Add-per-round-stack-trace-deduplication/20260618-025656]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Aaron-Tomlin/hung_task-Add-per-round-stack-trace-deduplication/20260814-211006
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20260620013559.1537893-1-atomlin%40atomlin.com
patch subject: [PATCH v2] hung_task: Add per-round stack trace deduplication
config: alpha-allmodconfig (https://download.01.org/0day-ci/archive/20260815/202608150327.OJ0wc1wA-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 16.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260815/202608150327.OJ0wc1wA-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202608150327.OJ0wc1wA-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from <command-line>:
   kernel/hung_task.c: In function 'check_hung_uninterruptible_tasks':
>> kernel/hung_task.c:388:72: error: 'sysctl_hung_task_dedup' undeclared (first use in this function); did you mean 'sysctl_hung_task_panic'?
     388 |         bool dedup_enabled = IS_ENABLED(CONFIG_STACKTRACE) ? READ_ONCE(sysctl_hung_task_dedup) : 0;
         |                                                                        ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler_types.h:682:23: note: in definition of macro '__compiletime_assert'
     682 |                 if (!(condition))                                       \
         |                       ^~~~~~~~~
   include/linux/compiler_types.h:702:9: note: in expansion of macro '_compiletime_assert'
     702 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
         |         ^~~~~~~~~~~~~~~~~~~
   include/asm-generic/rwonce.h:36:9: note: in expansion of macro 'compiletime_assert'
      36 |         compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),  \
         |         ^~~~~~~~~~~~~~~~~~
   include/asm-generic/rwonce.h:36:28: note: in expansion of macro '__native_word'
      36 |         compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),  \
         |                            ^~~~~~~~~~~~~
   include/asm-generic/rwonce.h:49:9: note: in expansion of macro 'compiletime_assert_rwonce_type'
      49 |         compiletime_assert_rwonce_type(x);                              \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   kernel/hung_task.c:388:62: note: in expansion of macro 'READ_ONCE'
     388 |         bool dedup_enabled = IS_ENABLED(CONFIG_STACKTRACE) ? READ_ONCE(sysctl_hung_task_dedup) : 0;
         |                                                              ^~~~~~~~~
   kernel/hung_task.c:388:72: note: each undeclared identifier is reported only once for each function it appears in
   include/linux/compiler_types.h:682:23: note: in definition of macro '__compiletime_assert'
     682 |                 if (!(condition))                                       \
         |                       ^~~~~~~~~
   include/linux/compiler_types.h:702:9: note: in expansion of macro '_compiletime_assert'
     702 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
         |         ^~~~~~~~~~~~~~~~~~~
   include/asm-generic/rwonce.h:36:9: note: in expansion of macro 'compiletime_assert'
      36 |         compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),  \
         |         ^~~~~~~~~~~~~~~~~~
   include/asm-generic/rwonce.h:36:28: note: in expansion of macro '__native_word'
      36 |         compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),  \
         |                            ^~~~~~~~~~~~~
   include/asm-generic/rwonce.h:49:9: note: in expansion of macro 'compiletime_assert_rwonce_type'
      49 |         compiletime_assert_rwonce_type(x);                              \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   kernel/hung_task.c:388:62: note: in expansion of macro 'READ_ONCE'
     388 |         bool dedup_enabled = IS_ENABLED(CONFIG_STACKTRACE) ? READ_ONCE(sysctl_hung_task_dedup) : 0;
         |                                                              ^~~~~~~~~


vim +388 kernel/hung_task.c

   375	
   376	/*
   377	 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
   378	 * a really long time. If that happens, print out a warning.
   379	 */
   380	static void check_hung_uninterruptible_tasks(unsigned long timeout)
   381	{
   382		int max_count = sysctl_hung_task_check_count;
   383		unsigned long last_break = jiffies;
   384		struct task_struct *g, *t;
   385		unsigned long this_round_count;
   386		int need_warning = sysctl_hung_task_warnings;
   387		unsigned long si_mask = hung_task_si_mask;
 > 388		bool dedup_enabled = IS_ENABLED(CONFIG_STACKTRACE) ? READ_ONCE(sysctl_hung_task_dedup) : 0;
   389	
   390		/*
   391		 * If the system crashed already then all bets are off,
   392		 * do not report extra hung tasks:
   393		 */
   394		if (test_taint(TAINT_DIE) || did_panic)
   395			return;
   396	
   397		/*
   398		 * Reset the de-duplicator hash table for this new detection round.
   399		 * This prevents stale hashes from permanently suppressing.
   400		 */
   401		if (dedup_enabled)
   402			hung_task_dedup_flush();
   403	
   404		this_round_count = 0;
   405		rcu_read_lock();
   406		for_each_process_thread(g, t) {
   407			if (!max_count--)
   408				goto unlock;
   409			if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
   410				if (!rcu_lock_break(g, t))
   411					goto unlock;
   412				last_break = jiffies;
   413			}
   414	
   415			if (task_is_hung(t, timeout)) {
   416				/*
   417				 * Increment the global counter so that userspace could
   418				 * start migrating tasks ASAP. But count the current
   419				 * round separately because userspace could reset
   420				 * the global counter at any time.
   421				 */
   422				atomic_long_inc(&sysctl_hung_task_detect_count);
   423				this_round_count++;
   424				hung_task_info(t, timeout, this_round_count, dedup_enabled);
   425			}
   426		}
   427	 unlock:
   428		rcu_read_unlock();
   429	
   430		if (!this_round_count)
   431			return;
   432	
   433		if (need_warning || hung_task_call_panic) {
   434			si_mask |= SYS_INFO_LOCKS;
   435	
   436			if (sysctl_hung_task_all_cpu_backtrace)
   437				si_mask |= SYS_INFO_ALL_BT;
   438		}
   439	
   440		sys_info(si_mask);
   441	
   442		if (hung_task_call_panic)
   443			panic("hung_task: blocked tasks");
   444	}
   445	

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