[PATCH 0/2] hung_task: Dump the blocking task stacktrace

[Masami Hiramatsu (Google)]

Hi,

The hung_task detector is very useful for detecting the lockup.
However, since it only dumps the blocked (uninterruptible sleep)
processes, it is not enough to identify the root cause of that
lockup.

For example, if a process holds a mutex and sleep an event in
interruptible state long time, the other processes will wait on
the mutex in uninterruptible state. In this case, the waiter
processes are dumped, but the blocker process is not shown
because it is sleep in interruptible state.

This adds a feature to dump the blocker task which holds a mutex
when detecting a hung task. e.g.

 INFO: task cat:113 blocked for more than 122 seconds.
       Not tainted 6.14.0-rc3-00002-g6afe972e1b9b #152
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 task:cat             state:D stack:13432 pid:113   tgid:113   ppid:103    task_flags:0x400100 flags:0x00000002
 Call Trace:
  <TASK>
  __schedule+0x731/0x960
  ? schedule_preempt_disabled+0x54/0xa0
  schedule+0xb7/0x140
  ? __mutex_lock+0x51d/0xa50
  ? __mutex_lock+0x51d/0xa50
  schedule_preempt_disabled+0x54/0xa0
  __mutex_lock+0x51d/0xa50
  ? current_time+0x3a/0x120
  read_dummy+0x23/0x70
  full_proxy_read+0x6a/0xc0
  vfs_read+0xc2/0x340
  ? __pfx_direct_file_splice_eof+0x10/0x10
  ? do_sendfile+0x1bd/0x2e0
  ksys_read+0x76/0xe0
  do_syscall_64+0xe3/0x1c0
  ? exc_page_fault+0xa9/0x1d0
  entry_SYSCALL_64_after_hwframe+0x77/0x7f
 RIP: 0033:0x4840cd
 RSP: 002b:00007ffe632b76c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
 RDX: 0000000000001000 RSI: 00007ffe632b7710 RDI: 0000000000000003
 RBP: 00007ffe632b7710 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
 R13: 000000003a8b63a0 R14: 0000000000000001 R15: ffffffffffffffff
  </TASK>
 INFO: task cat:113 is blocked on a mutex owned by task cat:112.
 task:cat             state:S stack:13432 pid:112   tgid:112   ppid:103    task_flags:0x400100 flags:0x00000002
 Call Trace:
  <TASK>
  __schedule+0x731/0x960
  ? schedule_timeout+0xa8/0x120
  schedule+0xb7/0x140
  schedule_timeout+0xa8/0x120
  ? __pfx_process_timeout+0x10/0x10
  msleep_interruptible+0x3e/0x60
  read_dummy+0x2d/0x70
  full_proxy_read+0x6a/0xc0
  vfs_read+0xc2/0x340
  ? __pfx_direct_file_splice_eof+0x10/0x10
  ? do_sendfile+0x1bd/0x2e0
  ksys_read+0x76/0xe0
  do_syscall_64+0xe3/0x1c0
  ? exc_page_fault+0xa9/0x1d0
  entry_SYSCALL_64_after_hwframe+0x77/0x7f
 RIP: 0033:0x4840cd
 RSP: 002b:00007ffd69513748 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
 RDX: 0000000000001000 RSI: 00007ffd69513790 RDI: 0000000000000003
 RBP: 00007ffd69513790 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
 R13: 0000000029d8d3a0 R14: 0000000000000001 R15: ffffffffffffffff
  </TASK>

Thank you,

---

Masami Hiramatsu (Google) (2):
      hung_task: Show the blocker task if the task is hung on mutex
      samples: Add hung_task detector mutex blocking sample


 kernel/hung_task.c                  |   38 ++++++++++++++++++++
 kernel/locking/mutex-debug.c        |    1 +
 kernel/locking/mutex.c              |    9 +++++
 kernel/locking/mutex.h              |    6 +++
 samples/Kconfig                     |    9 +++++
 samples/Makefile                    |    1 +
 samples/hung_task/Makefile          |    2 +
 samples/hung_task/hung_task_mutex.c |   66 +++++++++++++++++++++++++++++++++++
 8 files changed, 132 insertions(+)
 create mode 100644 samples/hung_task/Makefile
 create mode 100644 samples/hung_task/hung_task_mutex.c

--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>