From nobody Fri Dec 19 22:04:13 2025 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5A497253925 for ; Mon, 2 Jun 2025 22:10:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748902215; cv=none; b=XXjWuwKHJ5KbUc25dGxPHFtwclXubDmvg7QPhe1HjJtNxZidGP2shZCEIPKlSvCipB8Znoy3EJ3Q65wvxaMZvm/h2DgzEL3xjEAMvJr2R0GRq86qmJLCEN1M45F+ay8DJSWiPoZ7ahGeIQb65NMTAfTT+8SMxMFFrd9N4jP8Mcw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748902215; c=relaxed/simple; bh=OkTokFNzR+LTbaIJWldwGZ6txslRJOqJ0K87LQ2wW/o=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=mEBWGDPK45uqC9764Wl198m2RYBXFCYaLRdiDCw/1fwO02kmsAjk1xT+2zN0PF0/n9n75h9uWd5v4gAI6mVl2S7jJOa6T29Mg/aEoSuCy04BHKvlwQYQS70cSFM7yGGXKn2FqXkJXpGnb7XLTuYlvgqMBxurf6xziwSmJpGKcoE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=sl89SrbW; arc=none smtp.client-ip=209.85.210.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="sl89SrbW" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-747dd44048cso1534732b3a.3 for ; Mon, 02 Jun 2025 15:10:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1748902212; x=1749507012; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=2sC/PRtt/GMghRvne2VHFN9fc1yA9k6PjaGt1peEfjQ=; b=sl89SrbWQxHXmB18DuPwQWGWOMa9inli4d7BYl9JfttwuI7Mkm/5DEitktQnWs9Szz 2nRlPAHNV1J0G92IsUpDUXwRaYtjpHh5MdrVESq3bSUoW4oHLlB8Up+BNqZknlqQlqE5 MnWRtc5WTPkQvdTlwuAs5qJo8N/sfcmV3YRGt+/fQdmx7dioWCTHEWtC9pkS82AKV7Tu CronhRPeuGO84WjKp6ujMMRJyr8nALhy/oXqlfN8GIqAXEXZL8xMbWCV4o9peGzFcmOZ utHLmKKQR+7BhVexh5OeTNM9pKRV3RgKSgH+zwawbp0+Ztu7ZdPIZmul4e7PfIv+Djy4 5fEg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1748902212; x=1749507012; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=2sC/PRtt/GMghRvne2VHFN9fc1yA9k6PjaGt1peEfjQ=; b=ijZ7Uln46gvzR1Ztjz/TKFUKi+42Ksjl+t3o3BYOJx5jI6o9BLTspNbNWgC4m/ffoY ET/5xF7iNti0GYw6SHKnGZpJ5uiV6WjYPRCSeBRN2t9450/U2sjkULRfxqWYPShgVKzB 8p+8Oo2r5gjdUOBD+jEn6DPovaBK8PTBmB9yugPWm/sK9RaXvjvbGu6M6EMGTBBL7RY4 gliNYemQ8UcbbuSZSUOw7dnjHorhqga5faO7JKHB1yDJKf+RtLuup2Leo8Lbmn2y1d6a +HhNeK6iYUrDG0GHg08tPLdszgqEEeyG5Z2paC4rLTc3nEgIwedRjhBnnWVRs2BCGFSw /iww== X-Gm-Message-State: AOJu0YwBQyriDUyKYs+rZkM/HBotuYAsWoBbAuM+hB3yGxU+tJ9i5v1d XEK0xZVdbU/8XBtClcfDmGMoDdnCmmsfiZkDZ9drBUxnPCExRJsvF/IenuG/s/7RGyivFw1XvOn yv2KpOv0H/JS/UI0VA3OXV8TwD6qzAX/JEhOwydx3yel9HD1FpsNeTR9HUG8TtfAwZ1HrUHUSN/ dt4wWdNx9SgQ3qxeOyYwWobuTGgyA7KqjUdhO2QmnAhpTjw0An X-Google-Smtp-Source: AGHT+IHvp0410Sj38/s1im9oXm2RDdvYFiuB0p4E/ZBPsdhlxpaPfet3zRpavKUfmuTPdMx1ZvRozcZ2zp8V X-Received: from pfqn13.prod.google.com ([2002:aa7:984d:0:b0:746:2f7e:f86d]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:a10e:b0:21a:de8e:5e6d with SMTP id adf61e73a8af0-21adff3c891mr21263992637.8.1748902211805; Mon, 02 Jun 2025 15:10:11 -0700 (PDT) Date: Mon, 2 Jun 2025 22:09:50 +0000 In-Reply-To: <20250602221004.3837674-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250602221004.3837674-1-jstultz@google.com> X-Mailer: git-send-email 2.49.0.1204.g71687c7c1d-goog Message-ID: <20250602221004.3837674-4-jstultz@google.com> Subject: [RESEND][PATCH v17 3/8] locking/mutex: Add p->blocked_on wrappers for correctness checks From: John Stultz To: LKML Cc: Valentin Schneider , "Connor O'Brien" , John Stultz , Joel Fernandes , Qais Yousef , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Zimuzo Ezeozue , Mel Gorman , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kernel-team@android.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Valentin Schneider This lets us assert mutex::wait_lock is held whenever we access p->blocked_on, as well as warn us for unexpected state changes. Signed-off-by: Valentin Schneider [fix conflicts, call in more places] Signed-off-by: Connor O'Brien [jstultz: tweaked commit subject, reworked a good bit] Signed-off-by: John Stultz --- v2: * Added get_task_blocked_on() accessor v4: * Address READ_ONCE usage that was dropped in v2 * Reordered to be a later add on to the main patch series as Peter was unhappy with similar wrappers in other patches. v5: * Added some extra correctness checking in wrappers v7: * Tweaks to reorder this change in the patch series * Minor cleanup to set_task_blocked_on() suggested by Metin Kaya v15: * Split out into its own patch again. * Further improve assumption checks in helpers. v16: * Fix optimistic spin case that can call schedule() v17: * Fix typos caught by Metin Kaya * Add lockdep_assert_held_once and drop the READ_ONCE in __get_task_blocked_on(), as suggested by Juri Lelli Cc: Joel Fernandes Cc: Qais Yousef Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Valentin Schneider Cc: Steven Rostedt Cc: Ben Segall Cc: Zimuzo Ezeozue Cc: Mel Gorman Cc: Will Deacon Cc: Waiman Long Cc: Boqun Feng Cc: "Paul E. McKenney" Cc: Metin Kaya Cc: Xuewen Yan Cc: K Prateek Nayak Cc: Thomas Gleixner Cc: Daniel Lezcano Cc: Suleiman Souhlal Cc: kernel-team@android.com --- include/linux/sched.h | 54 ++++++++++++++++++++++++++++++++++-- kernel/locking/mutex-debug.c | 4 +-- kernel/locking/mutex.c | 32 ++++++++++----------- kernel/locking/ww_mutex.h | 6 ++-- 4 files changed, 70 insertions(+), 26 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 10be203ddb7e1..37c081be30ca6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -34,6 +34,7 @@ #include #include #include +#include #include #include #include @@ -2181,6 +2182,57 @@ extern int __cond_resched_rwlock_write(rwlock_t *loc= k); __cond_resched_rwlock_write(lock); \ }) =20 +static inline void __set_task_blocked_on(struct task_struct *p, struct mut= ex *m) +{ + WARN_ON_ONCE(!m); + /* The task should only be setting itself as blocked */ + WARN_ON_ONCE(p !=3D current); + /* Currently we serialize blocked_on under the mutex::wait_lock */ + lockdep_assert_held_once(&m->wait_lock); + /* + * Check ensure we don't overwrite existing mutex value + * with a different mutex. Note, setting it to the same + * lock repeatedly is ok. + */ + WARN_ON_ONCE(p->blocked_on && p->blocked_on !=3D m); + p->blocked_on =3D m; +} + +static inline void set_task_blocked_on(struct task_struct *p, struct mutex= *m) +{ + guard(raw_spinlock_irqsave)(&m->wait_lock); + __set_task_blocked_on(p, m); +} + +static inline void __clear_task_blocked_on(struct task_struct *p, struct m= utex *m) +{ + WARN_ON_ONCE(!m); + /* Currently we serialize blocked_on under the mutex::wait_lock */ + lockdep_assert_held_once(&m->wait_lock); + /* + * There may be cases where we re-clear already cleared + * blocked_on relationships, but make sure we are not + * clearing the relationship with a different lock. + */ + WARN_ON_ONCE(m && p->blocked_on && p->blocked_on !=3D m); + p->blocked_on =3D NULL; +} + +static inline void clear_task_blocked_on(struct task_struct *p, struct mut= ex *m) +{ + guard(raw_spinlock_irqsave)(&m->wait_lock); + __clear_task_blocked_on(p, m); +} + +static inline struct mutex *__get_task_blocked_on(struct task_struct *p) +{ + struct mutex *m =3D p->blocked_on; + + if (m) + lockdep_assert_held_once(&m->wait_lock); + return m; +} + static __always_inline bool need_resched(void) { return unlikely(tif_need_resched()); @@ -2220,8 +2272,6 @@ extern bool sched_task_on_rq(struct task_struct *p); extern unsigned long get_wchan(struct task_struct *p); extern struct task_struct *cpu_curr_snapshot(int cpu); =20 -#include - /* * In order to reduce various lock holder preemption latencies provide an * interface to see if a vCPU is currently running or not. diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index 758b7a6792b0c..949103fd8e9b5 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -54,13 +54,13 @@ void debug_mutex_add_waiter(struct mutex *lock, struct = mutex_waiter *waiter, lockdep_assert_held(&lock->wait_lock); =20 /* Current thread can't be already blocked (since it's executing!) */ - DEBUG_LOCKS_WARN_ON(task->blocked_on); + DEBUG_LOCKS_WARN_ON(__get_task_blocked_on(task)); } =20 void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *wa= iter, struct task_struct *task) { - struct mutex *blocked_on =3D READ_ONCE(task->blocked_on); + struct mutex *blocked_on =3D __get_task_blocked_on(task); =20 DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list)); DEBUG_LOCKS_WARN_ON(waiter->task !=3D task); diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 5243e59d75f40..ec39abbaae85a 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -643,8 +643,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas goto err_early_kill; } =20 - WARN_ON(current->blocked_on); - current->blocked_on =3D lock; + __set_task_blocked_on(current, lock); set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); for (;;) { @@ -684,9 +683,9 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas /* * As we likely have been woken up by task * that has cleared our blocked_on state, re-set - * it to the lock we are trying to aquire. + * it to the lock we are trying to acquire. */ - current->blocked_on =3D lock; + set_task_blocked_on(current, lock); set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -698,11 +697,15 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas =20 if (first) { trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); - /* clear blocked_on as mutex_optimistic_spin may schedule() */ - current->blocked_on =3D NULL; + /* + * mutex_optimistic_spin() can call schedule(), so + * clear blocked on so we don't become unselectable + * to run. + */ + clear_task_blocked_on(current, lock); if (mutex_optimistic_spin(lock, ww_ctx, &waiter)) break; - current->blocked_on =3D lock; + set_task_blocked_on(current, lock); trace_contention_begin(lock, LCB_F_MUTEX); } =20 @@ -710,7 +713,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas } raw_spin_lock_irqsave(&lock->wait_lock, flags); acquired: - current->blocked_on =3D NULL; + __clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); =20 if (ww_ctx) { @@ -740,11 +743,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas return 0; =20 err: - current->blocked_on =3D NULL; + __clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); __mutex_remove_waiter(lock, &waiter); err_early_kill: - WARN_ON(current->blocked_on); + WARN_ON(__get_task_blocked_on(current)); trace_contention_end(lock, ret); raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q); debug_mutex_free_waiter(&waiter); @@ -954,14 +957,7 @@ static noinline void __sched __mutex_unlock_slowpath(s= truct mutex *lock, unsigne next =3D waiter->task; =20 debug_mutex_wake_waiter(lock, waiter); - /* - * Unlock wakeups can be happening in parallel - * (when optimistic spinners steal and release - * the lock), so blocked_on may already be - * cleared here. - */ - WARN_ON(next->blocked_on && next->blocked_on !=3D lock); - next->blocked_on =3D NULL; + __clear_task_blocked_on(next, lock); wake_q_add(&wake_q, next); } =20 diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 00db40946328e..086fd5487ca77 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -289,9 +289,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER = *waiter, * blocked_on pointer. Otherwise we can see circular * blocked_on relationships that can't resolve. */ - WARN_ON(waiter->task->blocked_on && - waiter->task->blocked_on !=3D lock); - waiter->task->blocked_on =3D NULL; + __clear_task_blocked_on(waiter->task, lock); wake_q_add(wake_q, waiter->task); } =20 @@ -345,7 +343,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock, * blocked_on pointer. Otherwise we can see circular * blocked_on relationships that can't resolve. */ - owner->blocked_on =3D NULL; + __clear_task_blocked_on(owner, lock); wake_q_add(wake_q, owner); } return true; --=20 2.49.0.1204.g71687c7c1d-goog