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Aaron TomlinandAndrew Morton 73d40c42f6 hung_task: explicitly report I/O wait state in log output 
Currently, the hung task reporting mechanism indiscriminately labels all
TASK_UNINTERRUPTIBLE (D) tasks as "blocked", irrespective of whether they
are awaiting I/O completion or kernel locking primitives.  This ambiguity
compels system administrators to manually inspect stack traces to discern
whether the delay stems from an I/O wait (typically indicative of hardware
or filesystem anomalies) or software contention.  Such detailed analysis
is not always immediately accessible to system administrators or support
engineers.

To address this, this patch utilises the existing in_iowait field within
struct task_struct to augment the failure report.  If the task is blocked
due to I/O (e.g., via io_schedule_prepare()), the log message is updated
to explicitly state "blocked in I/O wait".

Examples:
        - Standard Block: "INFO: task bash:123 blocked for more than 120
          seconds".

        - I/O Block: "INFO: task dd:456 blocked in I/O wait for more than
          120 seconds".

Theoretically, concurrent executions of io_schedule_finish() could result
in a race condition where the read flag does not precisely correlate with
the subsequently printed backtrace.  However, this limitation is deemed
acceptable in practice.  The entire reporting mechanism is inherently racy
by design; nevertheless, it remains highly reliable in the vast majority
of cases, particularly because it primarily captures protracted stalls. 
Consequently, introducing additional synchronisation to mitigate this
minor inaccuracy would be entirely disproportionate to the situation.

Link: https://lkml.kernel.org/r/20260303221324.4106917-1-atomlin@atomlin.com
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-27 21:19:40 -07:00
Petr MladekandAndrew Morton 5eaef7f8ee hung_task: increment the global counter immediately 
A recent change allowed to reset the global counter of hung tasks using
the sysctl interface.  A potential race with the regular check has been
solved by updating the global counter only once at the end of the check.

However, the hung task check can take a significant amount of time,
particularly when task information is being dumped to slow serial
consoles.  Some users monitor this global counter to trigger immediate
migration of critical containers.  Delaying the increment until the full
check completes postpones these high-priority rescue operations.

Update the global counter as soon as a hung task is detected.  Since the
value is read asynchronously, a relaxed atomic operation is sufficient.

Link: https://lkml.kernel.org/r/20260303203031.4097316-4-atomlin@atomlin.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Reported-by: Lance Yang <lance.yang@linux.dev>
Closes: https://lore.kernel.org/r/f239e00f-4282-408d-b172-0f9885f4b01b@linux.dev
Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-27 21:19:40 -07:00
Aaron TomlinandAndrew Morton 49085e1b70 hung_task: enable runtime reset of hung_task_detect_count 
Currently, the hung_task_detect_count sysctl provides a cumulative count
of hung tasks since boot.  In long-running, high-availability
environments, this counter may lose its utility if it cannot be reset once
an incident has been resolved.  Furthermore, the previous implementation
relied upon implicit ordering, which could not strictly guarantee that
diagnostic metadata published by one CPU was visible to the panic logic on
another.

This patch introduces the capability to reset the detection count by
writing "0" to the hung_task_detect_count sysctl.  The proc_handler logic
has been updated to validate this input and atomically reset the counter.

The synchronisation of sysctl_hung_task_detect_count relies upon a
transactional model to ensure the integrity of the detection counter
against concurrent resets from userspace.  The application of
atomic_long_read_acquire() and atomic_long_cmpxchg_release() is correct
and provides the following guarantees:

    1. Prevention of Load-Store Reordering via Acquire Semantics By
       utilising atomic_long_read_acquire() to snapshot the counter
       before initiating the task traversal, we establish a strict
       memory barrier. This prevents the compiler or hardware from
       reordering the initial load to a point later in the scan. Without
       this "acquire" barrier, a delayed load could potentially read a
       "0" value resulting from a userspace reset that occurred
       mid-scan. This would lead to the subsequent cmpxchg succeeding
       erroneously, thereby overwriting the user's reset with stale
       increment data.

    2. Atomicity of the "Commit" Phase via Release Semantics The
       atomic_long_cmpxchg_release() serves as the transaction's commit
       point. The "release" barrier ensures that all diagnostic
       recordings and task-state observations made during the scan are
       globally visible before the counter is incremented.

    3. Race Condition Resolution This pairing effectively detects any
       "out-of-band" reset of the counter. If
       sysctl_hung_task_detect_count is modified via the procfs
       interface during the scan, the final cmpxchg will detect the
       discrepancy between the current value and the "acquire" snapshot.
       Consequently, the update will fail, ensuring that a reset command
       from the administrator is prioritised over a scan that may have
       been invalidated by that very reset.

Link: https://lkml.kernel.org/r/20260303203031.4097316-3-atomlin@atomlin.com
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Joel Granados <joel.granados@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-27 21:19:40 -07:00
Aaron TomlinandAndrew Morton 00b5cdeb9f hung_task: refactor detection logic and atomicise detection count 
Patch series "hung_task: Provide runtime reset interface for hung task
detector", v9.

This series introduces the ability to reset
/proc/sys/kernel/hung_task_detect_count.

Writing a "0" value to this file atomically resets the counter of detected
hung tasks.  This functionality provides system administrators with the
means to clear the cumulative diagnostic history following incident
resolution, thereby simplifying subsequent monitoring without
necessitating a system restart.


This patch (of 3):

The check_hung_task() function currently conflates two distinct
responsibilities: validating whether a task is hung and handling the
subsequent reporting (printing warnings, triggering panics, or
tracepoints).

This patch refactors the logic by introducing hung_task_info(), a function
dedicated solely to reporting.  The actual detection check,
task_is_hung(), is hoisted into the primary loop within
check_hung_uninterruptible_tasks().  This separation clearly decouples the
mechanism of detection from the policy of reporting.

Furthermore, to facilitate future support for concurrent hung task
detection, the global sysctl_hung_task_detect_count variable is converted
from unsigned long to atomic_long_t.  Consequently, the counting logic is
updated to accumulate the number of hung tasks locally (this_round_count)
during the iteration.  The global counter is then updated atomically via
atomic_long_cmpxchg_relaxed() once the loop concludes, rather than
incrementally during the scan.

These changes are strictly preparatory and introduce no functional change
to the system's runtime behaviour.

Link: https://lkml.kernel.org/r/20260303203031.4097316-1-atomlin@atomlin.com
Link: https://lkml.kernel.org/r/20260303203031.4097316-2-atomlin@atomlin.com
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Joel Granados <joel.granados@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-27 21:19:40 -07:00
Feng TangandAndrew Morton 8b2b9b4f6f hung_task: add hung_task_sys_info sysctl to dump sys info on task-hung 
When task-hung happens, developers may need different kinds of system
information (call-stacks, memory info, locks, etc.) to help debugging.

Add 'hung_task_sys_info' sysctl knob to take human readable string like
"tasks,mem,timers,locks,ftrace,...", and when task-hung happens, all
requested information will be dumped.  (refer kernel/sys_info.c for more
details).

Meanwhile, the newly introduced sys_info() call is used to unify some
existing info-dumping knobs.

[feng.tang@linux.alibaba.com: maintain consistecy established behavior, per Lance and Petr]
  Link: https://lkml.kernel.org/r/aRncJo1mA5Zk77Hr@U-2FWC9VHC-2323.local
Link: https://lkml.kernel.org/r/20251113111039.22701-3-feng.tang@linux.alibaba.com
Signed-off-by: Feng Tang <feng.tang@linux.alibaba.com>
Suggested-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-20 14:03:43 -08:00
Christoph HellwigandAndrew Morton af9b65d686 kernel/hung_task: unexport sysctl_hung_task_timeout_secs 
This was added by the bcachefs pull requests despite various
objections, and with bcachefs removed is now unused.

This reverts commit 5c3273ec3c ("kernel/hung_task.c: export
sysctl_hung_task_timeout_secs").

Link: https://lkml.kernel.org/r/20251104121920.2430568-1-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-20 14:03:41 -08:00
Li RongQingandAndrew Morton 9544f9e694 hung_task: panic when there are more than N hung tasks at the same time 
The hung_task_panic sysctl is currently a blunt instrument: it's all or
nothing.

Panicking on a single hung task can be an overreaction to a transient
glitch.  A more reliable indicator of a systemic problem is when
multiple tasks hang simultaneously.

Extend hung_task_panic to accept an integer threshold, allowing the
kernel to panic only when N hung tasks are detected in a single scan. 
This provides finer control to distinguish between isolated incidents
and system-wide failures.

The accepted values are:
- 0: Don't panic (unchanged)
- 1: Panic on the first hung task (unchanged)
- N > 1: Panic after N hung tasks are detected in a single scan

The original behavior is preserved for values 0 and 1, maintaining full
backward compatibility.

[lance.yang@linux.dev: new changelog]
Link: https://lkml.kernel.org/r/20251015063615.2632-1-lirongqing@baidu.com
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Tested-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Andrew Jeffery <andrew@codeconstruct.com.au> [aspeed_g5_defconfig]
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Florian Wesphal <fw@strlen.de>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-12 10:00:14 -08:00
Masami Hiramatsu (Google)andAndrew Morton 1440648c0f hung_task: dump blocker task if it is not hung 
Dump the lock blocker task if it is not hung because if the blocker task
is also hung, it should be dumped by the detector.  This will de-duplicate
the same stackdumps if the blocker task is also blocked by another task
(and hung).

Link: https://lkml.kernel.org/r/175391351423.688839.11917911323784986774.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Tested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-09-13 17:32:43 -07:00
Lance YangandAndrew Morton 77da18de55 hung_task: extend hung task blocker tracking to rwsems 
Inspired by mutex blocker tracking[1], and having already extended it to
semaphores, let's now add support for reader-writer semaphores (rwsems).

The approach is simple: when a task enters TASK_UNINTERRUPTIBLE while
waiting for an rwsem, we just call hung_task_set_blocker().  The hung task
detector can then query the rwsem's owner to identify the lock holder.

Tracking works reliably for writers, as there can only be a single writer
holding the lock, and its task struct is stored in the owner field.

The main challenge lies with readers.  The owner field points to only one
of many concurrent readers, so we might lose track of the blocker if that
specific reader unlocks, even while others remain.  This is not a
significant issue, however.  In practice, long-lasting lock contention is
almost always caused by a writer.  Therefore, reliably tracking the writer
is the primary goal of this patch series ;)

With this change, the hung task detector can now show blocker task's info
like below:

[Fri Jun 27 15:21:34 2025] INFO: task cat:28631 blocked for more than 122 seconds.
[Fri Jun 27 15:21:34 2025]       Tainted: G S                  6.16.0-rc3 #8
[Fri Jun 27 15:21:34 2025] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Fri Jun 27 15:21:34 2025] task:cat             state:D stack:0     pid:28631 tgid:28631 ppid:28501  task_flags:0x400000 flags:0x00004000
[Fri Jun 27 15:21:34 2025] Call Trace:
[Fri Jun 27 15:21:34 2025]  <TASK>
[Fri Jun 27 15:21:34 2025]  __schedule+0x7c7/0x1930
[Fri Jun 27 15:21:34 2025]  ? __pfx___schedule+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? policy_nodemask+0x215/0x340
[Fri Jun 27 15:21:34 2025]  ? _raw_spin_lock_irq+0x8a/0xe0
[Fri Jun 27 15:21:34 2025]  ? __pfx__raw_spin_lock_irq+0x10/0x10
[Fri Jun 27 15:21:34 2025]  schedule+0x6a/0x180
[Fri Jun 27 15:21:34 2025]  schedule_preempt_disabled+0x15/0x30
[Fri Jun 27 15:21:34 2025]  rwsem_down_read_slowpath+0x55e/0xe10
[Fri Jun 27 15:21:34 2025]  ? __pfx_rwsem_down_read_slowpath+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? __pfx___might_resched+0x10/0x10
[Fri Jun 27 15:21:34 2025]  down_read+0xc9/0x230
[Fri Jun 27 15:21:34 2025]  ? __pfx_down_read+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? __debugfs_file_get+0x14d/0x700
[Fri Jun 27 15:21:34 2025]  ? __pfx___debugfs_file_get+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? handle_pte_fault+0x52a/0x710
[Fri Jun 27 15:21:34 2025]  ? selinux_file_permission+0x3a9/0x590
[Fri Jun 27 15:21:34 2025]  read_dummy_rwsem_read+0x4a/0x90
[Fri Jun 27 15:21:34 2025]  full_proxy_read+0xff/0x1c0
[Fri Jun 27 15:21:34 2025]  ? rw_verify_area+0x6d/0x410
[Fri Jun 27 15:21:34 2025]  vfs_read+0x177/0xa50
[Fri Jun 27 15:21:34 2025]  ? __pfx_vfs_read+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? fdget_pos+0x1cf/0x4c0
[Fri Jun 27 15:21:34 2025]  ksys_read+0xfc/0x1d0
[Fri Jun 27 15:21:34 2025]  ? __pfx_ksys_read+0x10/0x10
[Fri Jun 27 15:21:34 2025]  do_syscall_64+0x66/0x2d0
[Fri Jun 27 15:21:34 2025]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Fri Jun 27 15:21:34 2025] RIP: 0033:0x7f3f8faefb40
[Fri Jun 27 15:21:34 2025] RSP: 002b:00007ffdeda5ab98 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Fri Jun 27 15:21:34 2025] RAX: ffffffffffffffda RBX: 0000000000010000 RCX: 00007f3f8faefb40
[Fri Jun 27 15:21:34 2025] RDX: 0000000000010000 RSI: 00000000010fa000 RDI: 0000000000000003
[Fri Jun 27 15:21:34 2025] RBP: 00000000010fa000 R08: 0000000000000000 R09: 0000000000010fff
[Fri Jun 27 15:21:34 2025] R10: 00007ffdeda59fe0 R11: 0000000000000246 R12: 00000000010fa000
[Fri Jun 27 15:21:34 2025] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000fff
[Fri Jun 27 15:21:34 2025]  </TASK>
[Fri Jun 27 15:21:34 2025] INFO: task cat:28631 <reader> blocked on an rw-semaphore likely owned by task cat:28630 <writer>
[Fri Jun 27 15:21:34 2025] task:cat             state:S stack:0     pid:28630 tgid:28630 ppid:28501  task_flags:0x400000 flags:0x00004000
[Fri Jun 27 15:21:34 2025] Call Trace:
[Fri Jun 27 15:21:34 2025]  <TASK>
[Fri Jun 27 15:21:34 2025]  __schedule+0x7c7/0x1930
[Fri Jun 27 15:21:34 2025]  ? __pfx___schedule+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? __mod_timer+0x304/0xa80
[Fri Jun 27 15:21:34 2025]  schedule+0x6a/0x180
[Fri Jun 27 15:21:34 2025]  schedule_timeout+0xfb/0x230
[Fri Jun 27 15:21:34 2025]  ? __pfx_schedule_timeout+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? __pfx_process_timeout+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? down_write+0xc4/0x140
[Fri Jun 27 15:21:34 2025]  msleep_interruptible+0xbe/0x150
[Fri Jun 27 15:21:34 2025]  read_dummy_rwsem_write+0x54/0x90
[Fri Jun 27 15:21:34 2025]  full_proxy_read+0xff/0x1c0
[Fri Jun 27 15:21:34 2025]  ? rw_verify_area+0x6d/0x410
[Fri Jun 27 15:21:34 2025]  vfs_read+0x177/0xa50
[Fri Jun 27 15:21:34 2025]  ? __pfx_vfs_read+0x10/0x10
[Fri Jun 27 15:21:34 2025]  ? fdget_pos+0x1cf/0x4c0
[Fri Jun 27 15:21:34 2025]  ksys_read+0xfc/0x1d0
[Fri Jun 27 15:21:34 2025]  ? __pfx_ksys_read+0x10/0x10
[Fri Jun 27 15:21:34 2025]  do_syscall_64+0x66/0x2d0
[Fri Jun 27 15:21:34 2025]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Fri Jun 27 15:21:34 2025] RIP: 0033:0x7f8f288efb40
[Fri Jun 27 15:21:34 2025] RSP: 002b:00007ffffb631038 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Fri Jun 27 15:21:34 2025] RAX: ffffffffffffffda RBX: 0000000000010000 RCX: 00007f8f288efb40
[Fri Jun 27 15:21:34 2025] RDX: 0000000000010000 RSI: 000000002a4b5000 RDI: 0000000000000003
[Fri Jun 27 15:21:34 2025] RBP: 000000002a4b5000 R08: 0000000000000000 R09: 0000000000010fff
[Fri Jun 27 15:21:34 2025] R10: 00007ffffb630460 R11: 0000000000000246 R12: 000000002a4b5000
[Fri Jun 27 15:21:34 2025] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000fff
[Fri Jun 27 15:21:34 2025]  </TASK>

[1] https://lore.kernel.org/all/174046694331.2194069.15472952050240807469.stgit@mhiramat.tok.corp.google.com/

Link: https://lkml.kernel.org/r/20250627072924.36567-3-lance.yang@linux.dev
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Mingzhe Yang <mingzhe.yang@ly.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yongliang Gao <leonylgao@tencent.com>
Cc: Zi Li <zi.li@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-07-19 19:08:26 -07:00
Lance YangandAndrew Morton 194a9b9e84 hung_task: show the blocker task if the task is hung on semaphore 
Inspired by mutex blocker tracking[1], this patch makes a trade-off to
balance the overhead and utility of the hung task detector.

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:

[Tue Apr  8 12:19:07 2025] INFO: task cat:945 blocked for more than 120 seconds.
[Tue Apr  8 12:19:07 2025]       Tainted: G            E      6.14.0-rc6+ #1
[Tue Apr  8 12:19:07 2025] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Tue Apr  8 12:19:07 2025] task:cat             state:D stack:0     pid:945   tgid:945   ppid:828    task_flags:0x400000 flags:0x00000000
[Tue Apr  8 12:19:07 2025] Call Trace:
[Tue Apr  8 12:19:07 2025]  <TASK>
[Tue Apr  8 12:19:07 2025]  __schedule+0x491/0xbd0
[Tue Apr  8 12:19:07 2025]  schedule+0x27/0xf0
[Tue Apr  8 12:19:07 2025]  schedule_timeout+0xe3/0xf0
[Tue Apr  8 12:19:07 2025]  ? __folio_mod_stat+0x2a/0x80
[Tue Apr  8 12:19:07 2025]  ? set_ptes.constprop.0+0x27/0x90
[Tue Apr  8 12:19:07 2025]  __down_common+0x155/0x280
[Tue Apr  8 12:19:07 2025]  down+0x53/0x70
[Tue Apr  8 12:19:07 2025]  read_dummy_semaphore+0x23/0x60
[Tue Apr  8 12:19:07 2025]  full_proxy_read+0x5f/0xa0
[Tue Apr  8 12:19:07 2025]  vfs_read+0xbc/0x350
[Tue Apr  8 12:19:07 2025]  ? __count_memcg_events+0xa5/0x140
[Tue Apr  8 12:19:07 2025]  ? count_memcg_events.constprop.0+0x1a/0x30
[Tue Apr  8 12:19:07 2025]  ? handle_mm_fault+0x180/0x260
[Tue Apr  8 12:19:07 2025]  ksys_read+0x66/0xe0
[Tue Apr  8 12:19:07 2025]  do_syscall_64+0x51/0x120
[Tue Apr  8 12:19:07 2025]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Tue Apr  8 12:19:07 2025] RIP: 0033:0x7f419478f46e
[Tue Apr  8 12:19:07 2025] RSP: 002b:00007fff1c4d2668 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Tue Apr  8 12:19:07 2025] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f419478f46e
[Tue Apr  8 12:19:07 2025] RDX: 0000000000020000 RSI: 00007f4194683000 RDI: 0000000000000003
[Tue Apr  8 12:19:07 2025] RBP: 00007f4194683000 R08: 00007f4194682010 R09: 0000000000000000
[Tue Apr  8 12:19:07 2025] R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000
[Tue Apr  8 12:19:07 2025] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[Tue Apr  8 12:19:07 2025]  </TASK>
[Tue Apr  8 12:19:07 2025] INFO: task cat:945 blocked on a semaphore likely last held by task cat:938
[Tue Apr  8 12:19:07 2025] task:cat             state:S stack:0     pid:938   tgid:938   ppid:584    task_flags:0x400000 flags:0x00000000
[Tue Apr  8 12:19:07 2025] Call Trace:
[Tue Apr  8 12:19:07 2025]  <TASK>
[Tue Apr  8 12:19:07 2025]  __schedule+0x491/0xbd0
[Tue Apr  8 12:19:07 2025]  ? _raw_spin_unlock_irqrestore+0xe/0x40
[Tue Apr  8 12:19:07 2025]  schedule+0x27/0xf0
[Tue Apr  8 12:19:07 2025]  schedule_timeout+0x77/0xf0
[Tue Apr  8 12:19:07 2025]  ? __pfx_process_timeout+0x10/0x10
[Tue Apr  8 12:19:07 2025]  msleep_interruptible+0x49/0x60
[Tue Apr  8 12:19:07 2025]  read_dummy_semaphore+0x2d/0x60
[Tue Apr  8 12:19:07 2025]  full_proxy_read+0x5f/0xa0
[Tue Apr  8 12:19:07 2025]  vfs_read+0xbc/0x350
[Tue Apr  8 12:19:07 2025]  ? __count_memcg_events+0xa5/0x140
[Tue Apr  8 12:19:07 2025]  ? count_memcg_events.constprop.0+0x1a/0x30
[Tue Apr  8 12:19:07 2025]  ? handle_mm_fault+0x180/0x260
[Tue Apr  8 12:19:07 2025]  ksys_read+0x66/0xe0
[Tue Apr  8 12:19:07 2025]  do_syscall_64+0x51/0x120
[Tue Apr  8 12:19:07 2025]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Tue Apr  8 12:19:07 2025] RIP: 0033:0x7f7c584a646e
[Tue Apr  8 12:19:07 2025] RSP: 002b:00007ffdba8ce158 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Tue Apr  8 12:19:07 2025] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f7c584a646e
[Tue Apr  8 12:19:07 2025] RDX: 0000000000020000 RSI: 00007f7c5839a000 RDI: 0000000000000003
[Tue Apr  8 12:19:07 2025] RBP: 00007f7c5839a000 R08: 00007f7c58399010 R09: 0000000000000000
[Tue Apr  8 12:19:07 2025] R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000
[Tue Apr  8 12:19:07 2025] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[Tue Apr  8 12:19:07 2025]  </TASK>

[1] https://lore.kernel.org/all/174046694331.2194069.15472952050240807469.stgit@mhiramat.tok.corp.google.com

Link: https://lkml.kernel.org/r/20250414145945.84916-3-ioworker0@gmail.com
Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yongliang Gao <leonylgao@tencent.com>
Cc: Zi Li <amaindex@outlook.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-05-11 17:54:08 -07:00
Lance YangandAndrew Morton e711faaafb hung_task: replace blocker_mutex with encoded blocker 
Patch series "hung_task: extend blocking task stacktrace dump to
semaphore", v5.

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:

[Tue Apr  8 12:19:07 2025] INFO: task cat:945 blocked for more than 120 seconds.
[Tue Apr  8 12:19:07 2025]       Tainted: G            E      6.14.0-rc6+ #1
[Tue Apr  8 12:19:07 2025] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Tue Apr  8 12:19:07 2025] task:cat             state:D stack:0     pid:945   tgid:945   ppid:828    task_flags:0x400000 flags:0x00000000
[Tue Apr  8 12:19:07 2025] Call Trace:
[Tue Apr  8 12:19:07 2025]  <TASK>
[Tue Apr  8 12:19:07 2025]  __schedule+0x491/0xbd0
[Tue Apr  8 12:19:07 2025]  schedule+0x27/0xf0
[Tue Apr  8 12:19:07 2025]  schedule_timeout+0xe3/0xf0
[Tue Apr  8 12:19:07 2025]  ? __folio_mod_stat+0x2a/0x80
[Tue Apr  8 12:19:07 2025]  ? set_ptes.constprop.0+0x27/0x90
[Tue Apr  8 12:19:07 2025]  __down_common+0x155/0x280
[Tue Apr  8 12:19:07 2025]  down+0x53/0x70
[Tue Apr  8 12:19:07 2025]  read_dummy_semaphore+0x23/0x60
[Tue Apr  8 12:19:07 2025]  full_proxy_read+0x5f/0xa0
[Tue Apr  8 12:19:07 2025]  vfs_read+0xbc/0x350
[Tue Apr  8 12:19:07 2025]  ? __count_memcg_events+0xa5/0x140
[Tue Apr  8 12:19:07 2025]  ? count_memcg_events.constprop.0+0x1a/0x30
[Tue Apr  8 12:19:07 2025]  ? handle_mm_fault+0x180/0x260
[Tue Apr  8 12:19:07 2025]  ksys_read+0x66/0xe0
[Tue Apr  8 12:19:07 2025]  do_syscall_64+0x51/0x120
[Tue Apr  8 12:19:07 2025]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Tue Apr  8 12:19:07 2025] RIP: 0033:0x7f419478f46e
[Tue Apr  8 12:19:07 2025] RSP: 002b:00007fff1c4d2668 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Tue Apr  8 12:19:07 2025] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f419478f46e
[Tue Apr  8 12:19:07 2025] RDX: 0000000000020000 RSI: 00007f4194683000 RDI: 0000000000000003
[Tue Apr  8 12:19:07 2025] RBP: 00007f4194683000 R08: 00007f4194682010 R09: 0000000000000000
[Tue Apr  8 12:19:07 2025] R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000
[Tue Apr  8 12:19:07 2025] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[Tue Apr  8 12:19:07 2025]  </TASK>
[Tue Apr  8 12:19:07 2025] INFO: task cat:945 blocked on a semaphore likely last held by task cat:938
[Tue Apr  8 12:19:07 2025] task:cat             state:S stack:0     pid:938   tgid:938   ppid:584    task_flags:0x400000 flags:0x00000000
[Tue Apr  8 12:19:07 2025] Call Trace:
[Tue Apr  8 12:19:07 2025]  <TASK>
[Tue Apr  8 12:19:07 2025]  __schedule+0x491/0xbd0
[Tue Apr  8 12:19:07 2025]  ? _raw_spin_unlock_irqrestore+0xe/0x40
[Tue Apr  8 12:19:07 2025]  schedule+0x27/0xf0
[Tue Apr  8 12:19:07 2025]  schedule_timeout+0x77/0xf0
[Tue Apr  8 12:19:07 2025]  ? __pfx_process_timeout+0x10/0x10
[Tue Apr  8 12:19:07 2025]  msleep_interruptible+0x49/0x60
[Tue Apr  8 12:19:07 2025]  read_dummy_semaphore+0x2d/0x60
[Tue Apr  8 12:19:07 2025]  full_proxy_read+0x5f/0xa0
[Tue Apr  8 12:19:07 2025]  vfs_read+0xbc/0x350
[Tue Apr  8 12:19:07 2025]  ? __count_memcg_events+0xa5/0x140
[Tue Apr  8 12:19:07 2025]  ? count_memcg_events.constprop.0+0x1a/0x30
[Tue Apr  8 12:19:07 2025]  ? handle_mm_fault+0x180/0x260
[Tue Apr  8 12:19:07 2025]  ksys_read+0x66/0xe0
[Tue Apr  8 12:19:07 2025]  do_syscall_64+0x51/0x120
[Tue Apr  8 12:19:07 2025]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[Tue Apr  8 12:19:07 2025] RIP: 0033:0x7f7c584a646e
[Tue Apr  8 12:19:07 2025] RSP: 002b:00007ffdba8ce158 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[Tue Apr  8 12:19:07 2025] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f7c584a646e
[Tue Apr  8 12:19:07 2025] RDX: 0000000000020000 RSI: 00007f7c5839a000 RDI: 0000000000000003
[Tue Apr  8 12:19:07 2025] RBP: 00007f7c5839a000 R08: 00007f7c58399010 R09: 0000000000000000
[Tue Apr  8 12:19:07 2025] R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000
[Tue Apr  8 12:19:07 2025] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[Tue Apr  8 12:19:07 2025]  </TASK>


This patch (of 3):

This patch replaces 'struct mutex *blocker_mutex' with 'unsigned long
blocker', as only one blocker is active at a time.

The blocker filed can store both the lock addrees and the lock type, with
LSB used to encode the type as Masami suggested, making it easier to
extend the feature to cover other types of locks.

Also, once the lock type is determined, we can directly extract the
address and cast it to a lock pointer ;)

Link: https://lkml.kernel.org/r/20250414145945.84916-1-ioworker0@gmail.com
Link: https://lore.kernel.org/all/174046694331.2194069.15472952050240807469.stgit@mhiramat.tok.corp.google.com [1]
Link: https://lkml.kernel.org/r/20250414145945.84916-2-ioworker0@gmail.com
Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yongliang Gao <leonylgao@tencent.com>
Cc: Zi Li <amaindex@outlook.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-05-11 17:54:07 -07:00
Masami Hiramatsu (Google)andAndrew Morton 3cf67d61ff hung_task: show the blocker task if the task is hung on mutex 
Patch series "hung_task: Dump the blocking task stacktrace", v4.

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:115 blocked for more than 122 seconds.
       Not tainted 6.14.0-rc3-00003-ga8946be3de00 #156
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 task:cat             state:D stack:13432 pid:115   tgid:115   ppid:106    task_flags:0x400100 flags:0x00000002
 Call Trace:
  <TASK>
  __schedule+0x731/0x960
  ? schedule_preempt_disabled+0x54/0xa0
  schedule+0xb7/0x140
  ? __mutex_lock+0x51b/0xa60
  ? __mutex_lock+0x51b/0xa60
  schedule_preempt_disabled+0x54/0xa0
  __mutex_lock+0x51b/0xa60
  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:00007ffe99071828 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
 RDX: 0000000000001000 RSI: 00007ffe99071870 RDI: 0000000000000003
 RBP: 00007ffe99071870 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
 R13: 00000000132fd3a0 R14: 0000000000000001 R15: ffffffffffffffff
  </TASK>
 INFO: task cat:115 is blocked on a mutex likely owned by task cat:114.
 task:cat             state:S stack:13432 pid:114   tgid:114   ppid:106    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:00007ffe3e0147b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
 RDX: 0000000000001000 RSI: 00007ffe3e014800 RDI: 0000000000000003
 RBP: 00007ffe3e014800 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
 R13: 000000001a0a93a0 R14: 0000000000000001 R15: ffffffffffffffff
  </TASK>

TBD: We can extend this feature to cover other locks like rwsem and
rt_mutex, but rwsem requires to dump all the tasks which acquire and wait
that rwsem.  We can follow the waiter link but the output will be a bit
different compared with mutex case.


This patch (of 2):

The "hung_task" shows a long-time uninterruptible slept task, but most
often, it's blocked on a mutex acquired by another task.  Without dumping
such a task, investigating the root cause of the hung task problem is very
difficult.

This introduce task_struct::blocker_mutex to point the mutex lock which
this task is waiting for.  Since the mutex has "owner" information, we can
find the owner task and dump it with hung tasks.

Note: the owner can be changed while dumping the owner task, so
this is "likely" the owner of the mutex.

With this change, the hung task shows blocker task's info like below;

 INFO: task cat:115 blocked for more than 122 seconds.
       Not tainted 6.14.0-rc3-00003-ga8946be3de00 #156
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 task:cat             state:D stack:13432 pid:115   tgid:115   ppid:106    task_flags:0x400100 flags:0x00000002
 Call Trace:
  <TASK>
  __schedule+0x731/0x960
  ? schedule_preempt_disabled+0x54/0xa0
  schedule+0xb7/0x140
  ? __mutex_lock+0x51b/0xa60
  ? __mutex_lock+0x51b/0xa60
  schedule_preempt_disabled+0x54/0xa0
  __mutex_lock+0x51b/0xa60
  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:00007ffe99071828 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
 RDX: 0000000000001000 RSI: 00007ffe99071870 RDI: 0000000000000003
 RBP: 00007ffe99071870 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
 R13: 00000000132fd3a0 R14: 0000000000000001 R15: ffffffffffffffff
  </TASK>
 INFO: task cat:115 is blocked on a mutex likely owned by task cat:114.
 task:cat             state:S stack:13432 pid:114   tgid:114   ppid:106    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:00007ffe3e0147b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
 RDX: 0000000000001000 RSI: 00007ffe3e014800 RDI: 0000000000000003
 RBP: 00007ffe3e014800 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
 R13: 000000001a0a93a0 R14: 0000000000000001 R15: ffffffffffffffff
  </TASK>

[akpm@linux-foundation.org: implement debug_show_blocker() in C rather than in CPP]
Link: https://lkml.kernel.org/r/174046694331.2194069.15472952050240807469.stgit@mhiramat.tok.corp.google.com
Link: https://lkml.kernel.org/r/174046695384.2194069.16796289525958195643.stgit@mhiramat.tok.corp.google.com
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Lance Yang <ioworker0@gmail.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Will Deacon <will@kernel.org>
Cc: Yongliang Gao <leonylgao@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-03-21 22:10:04 -07:00
Joel Granados 1751f872cc treewide: const qualify ctl_tables where applicable 
Add the const qualifier to all the ctl_tables in the tree except for
watchdog_hardlockup_sysctl, memory_allocation_profiling_sysctls,
loadpin_sysctl_table and the ones calling register_net_sysctl (./net,
drivers/inifiniband dirs). These are special cases as they use a
registration function with a non-const qualified ctl_table argument or
modify the arrays before passing them on to the registration function.

Constifying ctl_table structs will prevent the modification of
proc_handler function pointers as the arrays would reside in .rodata.
This is made possible after commit 78eb4ea25c ("sysctl: treewide:
constify the ctl_table argument of proc_handlers") constified all the
proc_handlers.

Created this by running an spatch followed by a sed command:
Spatch:
    virtual patch

    @
    depends on !(file in "net")
    disable optional_qualifier
    @

    identifier table_name != {
      watchdog_hardlockup_sysctl,
      iwcm_ctl_table,
      ucma_ctl_table,
      memory_allocation_profiling_sysctls,
      loadpin_sysctl_table
    };
    @@

    + const
    struct ctl_table table_name [] = { ... };

sed:
    sed --in-place \
      -e "s/struct ctl_table .table = &uts_kern/const struct ctl_table *table = \&uts_kern/" \
      kernel/utsname_sysctl.c

Reviewed-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> # for kernel/trace/
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> # SCSI
Reviewed-by: Darrick J. Wong <djwong@kernel.org> # xfs
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>
 2025-01-28 13:48:37 +01:00
Oxana KharitonovaandAndrew Morton 65ef17aa07 hung_task: add task->flags, blocked by coredump to log 
Resending this patch as I haven't received feedback on my initial
submission https://lore.kernel.org/all/20241204182953.10854-1-oxana@cloudflare.com/

For the processes which are terminated abnormally the kernel can provide
a coredump if enabled. When the coredump is performed, the process and
all its threads are put into the D state
(TASK_UNINTERRUPTIBLE | TASK_FREEZABLE).

On the other hand, we have kernel thread khungtaskd which monitors the
processes in the D state. If the task stuck in the D state more than
kernel.hung_task_timeout_secs, the hung_task alert appears in the kernel
log.

The higher memory usage of a process, the longer it takes to create
coredump, the longer tasks are in the D state. We have hung_task alerts
for the processes with memory usage above 10Gb. Although, our
kernel.hung_task_timeout_secs is 10 sec when the default is 120 sec.

Adding additional information to the log that the task is blocked by
coredump will help with monitoring. Another approach might be to
completely filter out alerts for such tasks, but in that case we would
lose transparency about what is putting pressure on some system
resources, e.g. we saw an increase in I/O when coredump occurs due its
writing to disk.

Additionally, it would be helpful to have task_struct->flags in the log
from the function sched_show_task(). Currently it prints
task_struct->thread_info->flags, this seems misleading as the line
starts with "task:xxxx".

[akpm@linux-foundation.org: fix printk control string]
Link: https://lkml.kernel.org/r/20250110160328.64947-1-oxana@cloudflare.com
Signed-off-by: Oxana Kharitonova <oxana@cloudflare.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ben Segall <bsegall@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-01-24 22:47:24 -08:00
Lance YangandAndrew Morton 03ecb24db2 hung_task: add detect count for hung tasks 
Patch series "add detect count for hung tasks", v2.

This patchset adds a counter, hung_task_detect_count, to track the number
of times hung tasks are detected.  

IHMO, hung tasks are a critical metric.  Currently, we detect them by
periodically parsing dmesg.  However, this method isn't as user-friendly
as using a counter.

Sometimes, a short-lived issue with NIC or hard drive can quickly decrease
the hung_task_warnings to zero.  Without warnings, we must directly access
the node to ensure that there are no more hung tasks and that the system
has recovered.  After all, load average alone cannot provide a clear
picture.

Once this counter is in place, in a high-density deployment pattern, we
plan to set hung_task_timeout_secs to a lower number to improve stability,
even though this might result in false positives.  And then we can set a
time-based threshold: if hung tasks last beyond this duration, we will
automatically migrate containers to other nodes.  Based on past
experience, this approach could help avoid many production disruptions.

Moreover, just like other important events such as OOM that already have
counters, having a dedicated counter for hung tasks makes sense ;)


This patch (of 2):

This commit adds a counter, hung_task_detect_count, to track the number of
times hung tasks are detected.

IHMO, hung tasks are a critical metric. Currently, we detect them by
periodically parsing dmesg. However, this method isn't as user-friendly as
using a counter.

Sometimes, a short-lived issue with NIC or hard drive can quickly decrease
the hung_task_warnings to zero. Without warnings, we must directly access
the node to ensure that there are no more hung tasks and that the system
has recovered. After all, load average alone cannot provide a clear
picture.

Once this counter is in place, in a high-density deployment pattern, we
plan to set hung_task_timeout_secs to a lower number to improve stability,
even though this might result in false positives. And then we can set a
time-based threshold: if hung tasks last beyond this duration, we will
automatically migrate containers to other nodes. Based on past experience,
this approach could help avoid many production disruptions.

Moreover, just like other important events such as OOM that already have
counters, having a dedicated counter for hung tasks makes sense.

[ioworker0@gmail.com: proc_doulongvec_minmax instead of proc_dointvec]
  Link: https://lkml.kernel.org/r/20241101114833.8377-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20241027120747.42833-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20241027120747.42833-2-ioworker0@gmail.com
Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Cc: Bang Li <libang.li@antgroup.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Huang Cun <cunhuang@tencent.com>
Cc: Joel Granados <j.granados@samsung.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: John Siddle <jsiddle@redhat.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Yongliang Gao <leonylgao@tencent.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2024-11-11 17:17:03 -08:00
Joel Granados 78eb4ea25c sysctl: treewide: constify the ctl_table argument of proc_handlers 
const qualify the struct ctl_table argument in the proc_handler function
signatures. This is a prerequisite to moving the static ctl_table
structs into .rodata data which will ensure that proc_handler function
pointers cannot be modified.

This patch has been generated by the following coccinelle script:

```
  virtual patch

  @r1@
  identifier ctl, write, buffer, lenp, ppos;
  identifier func !~ "appldata_(timer|interval)_handler|sched_(rt|rr)_handler|rds_tcp_skbuf_handler|proc_sctp_do_(hmac_alg|rto_min|rto_max|udp_port|alpha_beta|auth|probe_interval)";
  @@

  int func(
  - struct ctl_table *ctl
  + const struct ctl_table *ctl
    ,int write, void *buffer, size_t *lenp, loff_t *ppos);

  @r2@
  identifier func, ctl, write, buffer, lenp, ppos;
  @@

  int func(
  - struct ctl_table *ctl
  + const struct ctl_table *ctl
    ,int write, void *buffer, size_t *lenp, loff_t *ppos)
  { ... }

  @r3@
  identifier func;
  @@

  int func(
  - struct ctl_table *
  + const struct ctl_table *
    ,int , void *, size_t *, loff_t *);

  @r4@
  identifier func, ctl;
  @@

  int func(
  - struct ctl_table *ctl
  + const struct ctl_table *ctl
    ,int , void *, size_t *, loff_t *);

  @r5@
  identifier func, write, buffer, lenp, ppos;
  @@

  int func(
  - struct ctl_table *
  + const struct ctl_table *
    ,int write, void *buffer, size_t *lenp, loff_t *ppos);

```

* Code formatting was adjusted in xfs_sysctl.c to comply with code
  conventions. The xfs_stats_clear_proc_handler,
  xfs_panic_mask_proc_handler and xfs_deprecated_dointvec_minmax where
  adjusted.

* The ctl_table argument in proc_watchdog_common was const qualified.
  This is called from a proc_handler itself and is calling back into
  another proc_handler, making it necessary to change it as part of the
  proc_handler migration.

Co-developed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Co-developed-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: Joel Granados <j.granados@samsung.com>
 2024-07-24 20:59:29 +02:00
Yongliang GaoandAndrew Morton abd8ac0557 hung_task: ignore hung_task_warnings when hung_task_panic is enabled 
If hung_task_panic is enabled, don't consider the value of
hung_task_warnings and display the information of the hung tasks.

In some cases, hung_task_panic might not be initially set up, after
several hung tasks occur, the hung_task_warnings count reaches zero.  If
hung_task_panic is set up later, it may not display any helpful hung task
info in dmesg, only showing messages like:

Kernel panic - not syncing: hung_task: blocked tasks
CPU: 3 PID: 58 Comm: khungtaskd Not tainted 6.10.0-rc3 #19
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
Call Trace:
 <TASK>
 panic+0x2f3/0x320
 watchdog+0x2dd/0x510
 ? __pfx_watchdog+0x10/0x10
 kthread+0xe0/0x110
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x2f/0x40
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Link: https://lkml.kernel.org/r/20240613033159.3446265-1-leonylgao@gmail.com
Signed-off-by: Yongliang Gao <leonylgao@tencent.com>
Reviewed-by: Huang Cun <cunhuang@tencent.com>
Cc: Joel Granados <j.granados@samsung.com>
Cc: John Siddle <jsiddle@redhat.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2024-06-24 22:25:10 -07:00
Joel Granados 11a921909f kernel misc: Remove the now superfluous sentinel elements from ctl_table array 
This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which
will reduce the overall build time size of the kernel and run time
memory bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)

Remove the sentinel from ctl_table arrays. Reduce by one the values used
to compare the size of the adjusted arrays.

Signed-off-by: Joel Granados <j.granados@samsung.com>
 2024-04-24 09:43:53 +02:00
Kent Overstreet 5c3273ec3c kernel/hung_task.c: export sysctl_hung_task_timeout_secs 
needed for thread_with_file; also rare but not unheard of to need this
in module code, when blocking on user input.

one workaround used by some code is wait_event_interruptible() - but
that can be buggy if the outer context isn't expecting unwinding.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: fuyuanli <fuyuanli@didiglobal.com>
 2024-03-13 21:22:04 -04:00
Tom RixandAndrew Morton 882c5b261f kernel/hung_task.c: set some hung_task.c variables storage-class-specifier to static 
smatch reports several warnings
kernel/hung_task.c:31:19: warning:
  symbol 'sysctl_hung_task_check_count' was not declared. Should it be static?
kernel/hung_task.c:50:29: warning:
  symbol 'sysctl_hung_task_check_interval_secs' was not declared. Should it be static?
kernel/hung_task.c:52:19: warning:
  symbol 'sysctl_hung_task_warnings' was not declared. Should it be static?
kernel/hung_task.c:75:28: warning:
  symbol 'sysctl_hung_task_panic' was not declared. Should it be static?

These variables are only used in hung_task.c, so they should be static

Link: https://lkml.kernel.org/r/20230312164645.471259-1-trix@redhat.com
Signed-off-by: Tom Rix <trix@redhat.com>
Cc: Ben Dooks <ben.dooks@sifive.com>
Cc: fuyuanli <fuyuanli@didiglobal.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-04-08 13:45:37 -07:00
fuyuanliandAndrew Morton b1f712b308 hung_task: print message when hung_task_warnings gets down to zero. 
It's useful to report it when hung_task_warnings gets down to zero, so
that we can know if kernel log was lost or there is no hung task was
detected.

Link: https://lkml.kernel.org/r/20230201135416.GA6560@didi-ThinkCentre-M920t-N000
Signed-off-by: fuyuanli <fuyuanli@didiglobal.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-02-09 17:03:20 -08:00
Peter Zijlstra fdf756f712 sched: Fix more TASK_state comparisons 
Boris reported hung_task splats after commit 5aec788aeb ("sched: Fix
TASK_state comparisons"). Upon closer consideration of that change it
doesn't only exclude TASK_KILLABLE, but also TASK_IDLE.

Update the comment to reflect this fact and add an additional
TASK_NOLOAD test to exclude them.

Additionally, remove the TASK_FREEZABLE early exit from
check_hung_task(), a freezable task is not a frozen task.

Fixes: 5aec788aeb ("sched: Fix TASK_state comparisons")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Borislav Petkov <bp@alien8.de>
 2022-09-30 16:50:39 +02:00
Peter Zijlstra 5aec788aeb sched: Fix TASK_state comparisons 
Task state is fundamentally a bitmask; direct comparisons are probably
not working as intended. Specifically the normal wait-state have
a number of possible modifiers:

  TASK_UNINTERRUPTIBLE:	TASK_WAKEKILL, TASK_NOLOAD, TASK_FREEZABLE
  TASK_INTERRUPTIBLE:   TASK_FREEZABLE

Specifically, the addition of TASK_FREEZABLE wrecked
__wait_is_interruptible(). This however led to an audit of direct
comparisons yielding the rest of the changes.

Fixes: f5d39b0208 ("freezer,sched: Rewrite core freezer logic")
Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Debugged-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
 2022-09-28 10:00:16 +02:00
Peter Zijlstra f5d39b0208 freezer,sched: Rewrite core freezer logic 
Rewrite the core freezer to behave better wrt thawing and be simpler
in general.

By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is
ensured frozen tasks stay frozen until thawed and don't randomly wake
up early, as is currently possible.

As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up
two PF_flags (yay!).

Specifically; the current scheme works a little like:

	freezer_do_not_count();
	schedule();
	freezer_count();

And either the task is blocked, or it lands in try_to_freezer()
through freezer_count(). Now, when it is blocked, the freezer
considers it frozen and continues.

However, on thawing, once pm_freezing is cleared, freezer_count()
stops working, and any random/spurious wakeup will let a task run
before its time.

That is, thawing tries to thaw things in explicit order; kernel
threads and workqueues before doing bringing SMP back before userspace
etc.. However due to the above mentioned races it is entirely possible
for userspace tasks to thaw (by accident) before SMP is back.

This can be a fatal problem in asymmetric ISA architectures (eg ARMv9)
where the userspace task requires a special CPU to run.

As said; replace this with a special task state TASK_FROZEN and add
the following state transitions:

	TASK_FREEZABLE	-> TASK_FROZEN
	__TASK_STOPPED	-> TASK_FROZEN
	__TASK_TRACED	-> TASK_FROZEN

The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL
(IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state
is already required to deal with spurious wakeups and the freezer
causes one such when thawing the task (since the original state is
lost).

The special __TASK_{STOPPED,TRACED} states *can* be restored since
their canonical state is in ->jobctl.

With this, frozen tasks need an explicit TASK_FROZEN wakeup and are
free of undue (early / spurious) wakeups.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
 2022-09-07 21:53:50 +02:00
Ben Dooksandakpm 591c32bddb kernel/hung_task: fix address space of proc_dohung_task_timeout_secs 
The proc_dohung_task_timeout_secs() function is incorrectly marked
as having a __user buffer as argument 3. However this is not the
case and it is casing multiple sparse warnings. Fix the following
warnings by removing __user from the argument:

kernel/hung_task.c:237:52: warning: incorrect type in argument 3 (different address spaces)
kernel/hung_task.c:237:52:    expected void *
kernel/hung_task.c:237:52:    got void [noderef] __user *buffer
kernel/hung_task.c:287:35: warning: incorrect type in initializer (incompatible argument 3 (different address spaces))
kernel/hung_task.c:287:35:    expected int ( [usertype] *proc_handler )( ... )
kernel/hung_task.c:287:35:    got int ( * )( ... )
kernel/hung_task.c:295:35: warning: incorrect type in initializer (incompatible argument 3 (different address spaces))
kernel/hung_task.c:295:35:    expected int ( [usertype] *proc_handler )( ... )
kernel/hung_task.c:295:35:    got int ( * )( ... )

Link: https://lkml.kernel.org/r/20220714074744.189017-1-ben.dooks@sifive.com
Signed-off-by: Ben Dooks <ben.dooks@sifive.com>
Cc: <Conor.Dooley@microchip.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2022-07-29 18:12:35 -07:00