Re: [PATCH v2] hung_task: Add per-round stack trace deduplication
From: kernel test robot
Date: Fri Aug 14 2026 - 15:18:17 EST
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@xxxxxxxxx/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@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202608150327.OJ0wc1wA-lkp@xxxxxxxxx/
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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