From: Lance Yang <ioworker0@gmail.com>
To: akpm@linux-foundation.org
Cc: will@kernel.org, peterz@infradead.org, mingo@redhat.com,
longman@redhat.com, mhiramat@kernel.org,
anna.schumaker@oracle.com, boqun.feng@gmail.com,
joel.granados@kernel.org, kent.overstreet@linux.dev,
leonylgao@tencent.com, linux-kernel@vger.kernel.org,
rostedt@goodmis.org, senozhatsky@chromium.org,
tfiga@chromium.org, amaindex@outlook.com, jstultz@google.com,
Lance Yang <ioworker0@gmail.com>
Subject: [PATCH v4 0/3] hung_task: extend blocking task stacktrace dump to semaphore
Date: Thu, 20 Mar 2025 14:49:20 +0800 [thread overview]
Message-ID: <20250320064923.24000-1-ioworker0@gmail.com> (raw)
Hi all,
Inspired by mutex blocker tracking[1], this patch series extend the
feature to not only dump the blocker task holding a mutex but also to
support semaphores. Unlike mutexes, semaphores lack explicit ownership
tracking, making it challenging to identify the root cause of hangs. To
address this, we introduce a last_holder field to the semaphore structure,
which is updated when a task successfully calls down() and cleared during
up().
The assumption is that if a task is blocked on a semaphore, the holders
must not have released it. While this does not guarantee that the last
holder is one of the current blockers, it likely provides a practical hint
for diagnosing semaphore-related stalls.
With this change, the hung task detector can now show blocker task's info
like below:
[Thu Mar 20 04:52:21 2025] INFO: task cat:955 blocked for more than 120 seconds.
[Thu Mar 20 04:52:21 2025] Tainted: G E 6.14.0-rc6+ #1
[Thu Mar 20 04:52:21 2025] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Thu Mar 20 04:52:21 2025] task:cat state:D stack:0 pid:955 tgid:955 ppid:917 task_flags:0x400000 flags:0x00000000
[Thu Mar 20 04:52:21 2025] Call Trace:
[Thu Mar 20 04:52:21 2025] <TASK>
[Thu Mar 20 04:52:21 2025] __schedule+0x491/0xbd0
[Thu Mar 20 04:52:21 2025] schedule+0x27/0xf0
[Thu Mar 20 04:52:21 2025] schedule_timeout+0xe3/0xf0
[Thu Mar 20 04:52:21 2025] ? __folio_mod_stat+0x2a/0x80
[Thu Mar 20 04:52:21 2025] ? set_ptes.constprop.0+0x27/0x90
[Thu Mar 20 04:52:21 2025] __down_common+0x155/0x280
[Thu Mar 20 04:52:21 2025] down+0x53/0x70
[Thu Mar 20 04:52:21 2025] read_dummy_semaphore+0x23/0x60
[Thu Mar 20 04:52:21 2025] full_proxy_read+0x5f/0xa0
[Thu Mar 20 04:52:21 2025] vfs_read+0xbc/0x350
[Thu Mar 20 04:52:21 2025] ? __count_memcg_events+0xa5/0x140
[Thu Mar 20 04:52:21 2025] ? count_memcg_events.constprop.0+0x1a/0x30
[Thu Mar 20 04:52:21 2025] ? handle_mm_fault+0x180/0x260
[Thu Mar 20 04:52:21 2025] ksys_read+0x66/0xe0
[Thu Mar 20 04:52:21 2025] do_syscall_64+0x51/0x120
[Thu Mar 20 04:52:21 2025] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Thu Mar 20 04:52:21 2025] RIP: 0033:0x7ff96d4ab46e
[Thu Mar 20 04:52:21 2025] RSP: 002b:00007ffe2f47f3a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Thu Mar 20 04:52:21 2025] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007ff96d4ab46e
[Thu Mar 20 04:52:21 2025] RDX: 0000000000020000 RSI: 00007ff96d39f000 RDI: 0000000000000003
[Thu Mar 20 04:52:21 2025] RBP: 00007ff96d39f000 R08: 00007ff96d39e010 R09: 0000000000000000
[Thu Mar 20 04:52:21 2025] R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000
[Thu Mar 20 04:52:21 2025] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[Thu Mar 20 04:52:21 2025] </TASK>
[Thu Mar 20 04:52:21 2025] INFO: task cat:955 blocked on a semaphore likely last held by task cat:909
[Thu Mar 20 04:52:21 2025] task:cat state:S stack:0 pid:909 tgid:909 ppid:771 task_flags:0x400000 flags:0x00000000
[Thu Mar 20 04:52:21 2025] Call Trace:
[Thu Mar 20 04:52:21 2025] <TASK>
[Thu Mar 20 04:52:21 2025] __schedule+0x491/0xbd0
[Thu Mar 20 04:52:21 2025] ? _raw_spin_unlock_irqrestore+0xe/0x40
[Thu Mar 20 04:52:21 2025] schedule+0x27/0xf0
[Thu Mar 20 04:52:21 2025] schedule_timeout+0x77/0xf0
[Thu Mar 20 04:52:21 2025] ? __pfx_process_timeout+0x10/0x10
[Thu Mar 20 04:52:21 2025] msleep_interruptible+0x49/0x60
[Thu Mar 20 04:52:21 2025] read_dummy_semaphore+0x2d/0x60
[Thu Mar 20 04:52:21 2025] full_proxy_read+0x5f/0xa0
[Thu Mar 20 04:52:21 2025] vfs_read+0xbc/0x350
[Thu Mar 20 04:52:21 2025] ? __count_memcg_events+0xa5/0x140
[Thu Mar 20 04:52:21 2025] ? count_memcg_events.constprop.0+0x1a/0x30
[Thu Mar 20 04:52:21 2025] ? handle_mm_fault+0x180/0x260
[Thu Mar 20 04:52:21 2025] ksys_read+0x66/0xe0
[Thu Mar 20 04:52:21 2025] do_syscall_64+0x51/0x120
[Thu Mar 20 04:52:21 2025] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Thu Mar 20 04:52:21 2025] RIP: 0033:0x7fe6bf7a046e
[Thu Mar 20 04:52:21 2025] RSP: 002b:00007ffd6e1a4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Thu Mar 20 04:52:21 2025] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007fe6bf7a046e
[Thu Mar 20 04:52:21 2025] RDX: 0000000000020000 RSI: 00007fe6bf694000 RDI: 0000000000000003
[Thu Mar 20 04:52:21 2025] RBP: 00007fe6bf694000 R08: 00007fe6bf693010 R09: 0000000000000000
[Thu Mar 20 04:52:21 2025] R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000
[Thu Mar 20 04:52:21 2025] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[1] https://lore.kernel.org/all/174046694331.2194069.15472952050240807469.stgit@mhiramat.tok.corp.google.com
Thanks,
Lance
---
v3 -> v4:
* #01 #02 Pick RB from Masami - thanks!
* #03 Pick AB from Masami - thanks!
* Extract the type from the blocker and use a switch-case instead of
if-else, suggested by Masami
* https://lore.kernel.org/all/20250319081138.25133-1-ioworker0@gmail.com
v2 -> v3:
* Remove the unnecessary WARN_ON_ONCE check for 'current->blocker',
suggested by Masami
* Drop the redundant #ifdef for including the hung task header file,
suggested by Masam
* Unify the samples into 'hung_task_tests.c', suggested by Masami
* https://lore.kernel.org/all/20250314144300.32542-1-ioworker0@gmail.com
v1 -> v2:
* Use one field to store the blocker as only one is active at a time,
suggested by Masami
* Leverage the LSB of the blocker field to reduce memory footprint,
suggested by Masami
* Add a hung_task detector semaphore blocking test sample code
* https://lore.kernel.org/all/20250301055102.88746-1-ioworker0@gmail.com
Lance Yang (2):
hung_task: replace blocker_mutex with encoded blocker
hung_task: show the blocker task if the task is hung on semaphore
Zi Li (1):
samples: extend hung_task detector test with semaphore support
include/linux/hung_task.h | 99 +++++++++++++++++++++++++++++
include/linux/sched.h | 2 +-
include/linux/semaphore.h | 15 ++++-
kernel/hung_task.c | 55 ++++++++++++----
kernel/locking/mutex.c | 5 +-
kernel/locking/semaphore.c | 52 +++++++++++++--
samples/Kconfig | 9 +--
samples/hung_task/Makefile | 2 +-
samples/hung_task/hung_task_mutex.c | 66 -------------------
samples/hung_task/hung_task_tests.c | 97 ++++++++++++++++++++++++++++
10 files changed, 310 insertions(+), 92 deletions(-)
create mode 100644 include/linux/hung_task.h
delete mode 100644 samples/hung_task/hung_task_mutex.c
create mode 100644 samples/hung_task/hung_task_tests.c
--
2.45.2
next reply other threads:[~2025-03-20 6:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-20 6:49 Lance Yang [this message]
2025-03-20 6:49 ` [PATCH v4 1/3] hung_task: replace blocker_mutex with encoded blocker Lance Yang
2025-04-07 20:08 ` Andrew Morton
2025-04-08 12:29 ` Lance Yang
2025-03-20 6:49 ` [PATCH v4 2/3] hung_task: show the blocker task if the task is hung on semaphore Lance Yang
2025-04-07 20:08 ` Andrew Morton
2025-04-07 20:08 ` Andrew Morton
2025-04-08 12:27 ` Lance Yang
2025-03-20 6:49 ` [PATCH v4 3/3] samples: extend hung_task detector test with semaphore support Lance Yang
2025-04-07 20:08 ` [PATCH v4 0/3] hung_task: extend blocking task stacktrace dump to semaphore Andrew Morton
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