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Message-ID: <20250320064923.24000-1-ioworker0@gmail.com> Date: Thu, 20 Mar 2025 14:49:20 +0800 From: Lance Yang <ioworker0@...il.com> To: akpm@...ux-foundation.org Cc: will@...nel.org, peterz@...radead.org, mingo@...hat.com, longman@...hat.com, mhiramat@...nel.org, anna.schumaker@...cle.com, boqun.feng@...il.com, joel.granados@...nel.org, kent.overstreet@...ux.dev, leonylgao@...cent.com, linux-kernel@...r.kernel.org, rostedt@...dmis.org, senozhatsky@...omium.org, tfiga@...omium.org, amaindex@...look.com, jstultz@...gle.com, Lance Yang <ioworker0@...il.com> Subject: [PATCH v4 0/3] hung_task: extend blocking task stacktrace dump to semaphore 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
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