From nobody Fri Apr 17 09:26:56 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D67DC43217 for ; Mon, 21 Nov 2022 10:11:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231267AbiKUKLl (ORCPT ); Mon, 21 Nov 2022 05:11:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48536 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231253AbiKUKLX (ORCPT ); Mon, 21 Nov 2022 05:11:23 -0500 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15624E0DD for ; Mon, 21 Nov 2022 02:11:21 -0800 (PST) Received: from fsav411.sakura.ne.jp (fsav411.sakura.ne.jp [133.242.250.110]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 2ALAAwo4005126; Mon, 21 Nov 2022 19:10:59 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav411.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav411.sakura.ne.jp); Mon, 21 Nov 2022 19:10:58 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav411.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 2ALAAwFf005123 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Mon, 21 Nov 2022 19:10:58 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <41f43b27-d910-78e0-c0b3-f2885fe1cd22@I-love.SAKURA.ne.jp> Date: Mon, 21 Nov 2022 19:10:58 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Content-Language: en-US To: Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Andrew Morton Cc: LKML From: Tetsuo Handa Subject: [PATCH v2 (repost)] locking/lockdep: add debug_show_all_lock_holders() Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Currently, check_hung_uninterruptible_tasks() reports details of locks held in the system. Also, lockdep_print_held_locks() does not report details of locks held by a thread if that thread is in TASK_RUNNING state. Several years of experience of debugging without vmcore tells me that these limitations have been a barrier for understanding what went wrong in syzbot's "INFO: task hung in" reports. I initially thought that the cause of "INFO: task hung in" reports is due to over-stressing. But I understood that over-stressing is unlikely. I now consider that there likely is a deadlock/livelock bug where lockdep cannot report as a deadlock when "INFO: task hung in" is reported. A typical case is that thread-1 is waiting for something to happen (e.g. wait_event_*()) with a lock held. When thread-2 tries to hold that lock using e.g. mutex_lock(), check_hung_uninterruptible_tasks() reports that thread-2 is hung and thread-1 is holding a lock which thread-2 is trying to hold. But currently check_hung_uninterruptible_tasks() cannot report the exact location of thread-1 which gives us an important hint for understanding why thread-1 is holding that lock for so long period. When check_hung_uninterruptible_tasks() reports a thread waiting for a lock, it is important to report backtrace of threads which already held that lock. Therefore, allow check_hung_uninterruptible_tasks() to report the exact location of threads which is holding any lock. To deduplicate code, share debug_show_all_{locks,lock_holders}() using a flag. As a side effect of sharing, __debug_show_all_locks() skips current thread if the caller is holding no lock, for reporting RCU lock taken inside __debug_show_all_locks() is generally useless. Signed-off-by: Tetsuo Handa Acked-by: Waiman Long --- Changes in v2: Share debug_show_all_lock_holders() and debug_show_all_locks(), suggested by Waiman Long . include/linux/debug_locks.h | 17 ++++++++++++++++- kernel/hung_task.c | 2 +- kernel/locking/lockdep.c | 14 +++++++++++--- 3 files changed, 28 insertions(+), 5 deletions(-) diff --git a/include/linux/debug_locks.h b/include/linux/debug_locks.h index dbb409d77d4f..b45c89fadfe4 100644 --- a/include/linux/debug_locks.h +++ b/include/linux/debug_locks.h @@ -48,7 +48,18 @@ extern int debug_locks_off(void); #endif =20 #ifdef CONFIG_LOCKDEP -extern void debug_show_all_locks(void); +extern void __debug_show_all_locks(bool show_stack); + +static inline void debug_show_all_locks(void) +{ + __debug_show_all_locks(false); +} + +static inline void debug_show_all_lock_holders(void) +{ + __debug_show_all_locks(true); +} + extern void debug_show_held_locks(struct task_struct *task); extern void debug_check_no_locks_freed(const void *from, unsigned long len= ); extern void debug_check_no_locks_held(void); @@ -61,6 +72,10 @@ static inline void debug_show_held_locks(struct task_str= uct *task) { } =20 +static inline void debug_show_all_lock_holders(void) +{ +} + static inline void debug_check_no_locks_freed(const void *from, unsigned long len) { diff --git a/kernel/hung_task.c b/kernel/hung_task.c index c71889f3f3fc..5fba784258b7 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -213,7 +213,7 @@ static void check_hung_uninterruptible_tasks(unsigned l= ong timeout) unlock: rcu_read_unlock(); if (hung_task_show_lock) - debug_show_all_locks(); + debug_show_all_lock_holders(); =20 if (hung_task_show_all_bt) { hung_task_show_all_bt =3D false; diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index e3375bc40dad..b3da133825cc 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -55,6 +55,7 @@ #include #include #include +#include =20 #include =20 @@ -6487,7 +6488,7 @@ void debug_check_no_locks_held(void) EXPORT_SYMBOL_GPL(debug_check_no_locks_held); =20 #ifdef __KERNEL__ -void debug_show_all_locks(void) +void __debug_show_all_locks(bool show_stack) { struct task_struct *g, *p; =20 @@ -6495,12 +6496,19 @@ void debug_show_all_locks(void) pr_warn("INFO: lockdep is turned off.\n"); return; } - pr_warn("\nShowing all locks held in the system:\n"); + if (show_stack) + pr_warn("\nShowing all threads with locks held in the system:\n"); + else + pr_warn("\nShowing all locks held in the system:\n"); =20 rcu_read_lock(); for_each_process_thread(g, p) { if (!p->lockdep_depth) continue; + if (p =3D=3D current && p->lockdep_depth =3D=3D 1) + continue; + if (show_stack) + sched_show_task(p); lockdep_print_held_locks(p); touch_nmi_watchdog(); touch_all_softlockup_watchdogs(); @@ -6510,7 +6518,7 @@ void debug_show_all_locks(void) pr_warn("\n"); pr_warn("=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D\n\= n"); } -EXPORT_SYMBOL_GPL(debug_show_all_locks); +EXPORT_SYMBOL_GPL(__debug_show_all_locks); #endif =20 /* --=20 2.18.4