From nobody Thu Oct 2 00:49:10 2025 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 A06ED261573 for ; Fri, 26 Sep 2025 03:29:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857380; cv=none; b=hiSZVLgYTv/EYC3p5qpHIcig4B+gsV8rymLx7LfRm8OItuJAM9NmdG/aeIT9W+2UiEoBZjXJboctpHnjusoDFs+ClXVRp0TYRs7x5/0IrMGhVPRKXDpdMZsOBM6HECsxpt11kT+OzYNF2EP95qBMunGEv6PC2gxhyYv9YdeTefo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857380; c=relaxed/simple; bh=JtfAi5hWsh3uJOW3ZPAhF8I+1Yd0SMHHh4xc7fhhfUQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=KYgs147i5irBjBhUWhXw7NFxIzKEgJ8UnkPz7YfKw28FNBG2YtramwlDcvaJNSnZAaC5CqwPZSLeRSeUkUGY/7JhTBY3Pj71NuUOWTUzffXSZvn6crDk3AoLYz3BZ3IJXtsWoK6bobOBrXaP7da+RFHZuAoyQGSKKjE6TH9gDSk= 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=Z26pu3TO; arc=none smtp.client-ip=209.85.214.201 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="Z26pu3TO" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-244581953b8so17598335ad.2 for ; Thu, 25 Sep 2025 20:29:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1758857378; x=1759462178; 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=S6Qns3BtlUetjoWf4Xv2j7oWU8nUNLzVejhQGmPjFYo=; b=Z26pu3TO/Ia70awFYuJdTe9zvIQHiqkGLrxJmAWiCwh6xMXzdy3YwBNUEhJiGbUkKa /LKOfz2Kj2iHoTpmTpyMyJaLYlTU5RUurTGCO1Ozsivio4fULL1G7Z5qCQm47AaCZKFm dN+HQFwv6ASv+jQKgBx3T1QQx2Qlh/GXF89v71vpIn9944RNWeVT83Frnbhj8cCly8gJ bkpAKd2U9ozVfrB/tHcHToOO5/j17YmSBcTQaW0YQZ55A/T7mhsbjMe90AelxIz9f0tx eFhby+Lw89FlpBlnFtCecVBXOIfcBiK3Ny5d728kiGkvDdIoZ5ajKNBxNE3npWcAtfiB LdXg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758857378; x=1759462178; 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=S6Qns3BtlUetjoWf4Xv2j7oWU8nUNLzVejhQGmPjFYo=; b=iJkZcaRIxRVFCJBXT8Z+cLLw2Q+ILo592h2T9xJ07MZXOkGwow8dJYaFHp45R4gVN3 9GaFOPdVIIZeyQ1tT5qSkYR4kt386aeGdJy8NM51+LyEWrZZ2vN8OUJL1IbHDt1alXDQ GGfnhPxzeXHkWF2QtLMAp8kNZEcdG4NF0iOlU0AlbuZiMP/vXsxcDU+dLZo+TV1QE99K MxuAMY6xUda7FwvzkM3iQImI9cokMwzyUS2m6b8GIeOYvz0t8lE3kxSy2qddIZf28lL8 p3gA9Y0Ah42tF8F9Bv4wN3zurn/lc1/gWWYxo2OtvthxrVr9O2Qc11CDoJHuYm+nMpIS p7rg== X-Gm-Message-State: AOJu0YzGd2YvR1p28swBZsvtSdJh1zWRxAJZGoPe25zei9MxnB1THfwm wAALv8DOmTgdquYBVqijbGqIQmU2U+mGw8RJbl0PhdLfXt9GRDOSXCTZWjPDVOq4DNL3LMNdOUb /5wXl3iOIp9fpKVxL4YEkmJRgBsKWHj7buiO7kGIKpO/Jd9cLHa29SEbZhU8M1//SnkCZLuiR+v 9TrztjVQR+juvUAPdVJKkWkvlR6+ZgTGv3iSNNwUL9zx2pFD4o X-Google-Smtp-Source: AGHT+IE8WCtDtXoZb6+m4qTEuPGJA6sX6QzlbwF0/YgqXhsf/nd1+IEOzNlvS/T+PHDLnjDm7T26kS2XugYF X-Received: from pjbsx12.prod.google.com ([2002:a17:90b:2ccc:b0:32d:def7:e60f]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:3850:b0:267:9a29:7800 with SMTP id d9443c01a7336-27ed4ae4927mr67161835ad.59.1758857377761; Thu, 25 Sep 2025 20:29:37 -0700 (PDT) Date: Fri, 26 Sep 2025 03:29:09 +0000 In-Reply-To: <20250926032931.27663-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250926032931.27663-1-jstultz@google.com> X-Mailer: git-send-email 2.51.0.536.g15c5d4f767-goog Message-ID: <20250926032931.27663-2-jstultz@google.com> Subject: [PATCH v22 1/6] locking: Add task::blocked_lock to serialize blocked_on state From: John Stultz To: LKML Cc: John Stultz , K Prateek Nayak , 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 , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kuyo chang , hupu , kernel-team@android.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" So far, we have been able to utilize the mutex::wait_lock for serializing the blocked_on state, but when we move to proxying across runqueues, we will need to add more state and a way to serialize changes to this state in contexts where we don't hold the mutex::wait_lock. So introduce the task::blocked_lock, which nests under the mutex::wait_lock in the locking order, and rework the locking to use it. Signed-off-by: John Stultz Reviewed-by: K Prateek Nayak --- v15: * Split back out into later in the series v16: * Fixups to mark tasks unblocked before sleeping in mutex_optimistic_spin() * Rework to use guard() as suggested by Peter v19: * Rework logic for PREEMPT_RT issues reported by K Prateek Nayak v21: * After recently thinking more on ww_mutex code, I reworked the blocked_lock usage in mutex lock to avoid having to take nested locks in the ww_mutex paths, as I was concerned the lock ordering constraints weren't as strong as I had previously thought. v22: * Added some extra spaces to avoid dense code blocks suggested by K Prateek 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: kuyo chang Cc: hupu Cc: kernel-team@android.com --- include/linux/sched.h | 52 +++++++++++++++--------------------- init/init_task.c | 1 + kernel/fork.c | 1 + kernel/locking/mutex-debug.c | 4 +-- kernel/locking/mutex.c | 40 +++++++++++++++++---------- kernel/locking/ww_mutex.h | 4 +-- kernel/sched/core.c | 4 ++- 7 files changed, 57 insertions(+), 49 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index e4ce0a76831e5..cb4e81d9d9b67 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1233,6 +1233,7 @@ struct task_struct { #endif =20 struct mutex *blocked_on; /* lock we're blocked on */ + raw_spinlock_t blocked_lock; =20 #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER /* @@ -2141,57 +2142,48 @@ extern int __cond_resched_rwlock_write(rwlock_t *lo= ck); #ifndef CONFIG_PREEMPT_RT static inline struct mutex *__get_task_blocked_on(struct task_struct *p) { - struct mutex *m =3D p->blocked_on; + lockdep_assert_held_once(&p->blocked_lock); + return p->blocked_on; +} =20 - if (m) - lockdep_assert_held_once(&m->wait_lock); - return m; +static inline struct mutex *get_task_blocked_on(struct task_struct *p) +{ + guard(raw_spinlock_irqsave)(&p->blocked_lock); + return __get_task_blocked_on(p); } =20 static inline void __set_task_blocked_on(struct task_struct *p, struct mut= ex *m) { - struct mutex *blocked_on =3D READ_ONCE(p->blocked_on); - 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); + /* Currently we serialize blocked_on under the task::blocked_lock */ + lockdep_assert_held_once(&p->blocked_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(blocked_on && blocked_on !=3D m); - WRITE_ONCE(p->blocked_on, 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); + WARN_ON_ONCE(p->blocked_on && p->blocked_on !=3D m); + p->blocked_on =3D m; } =20 static inline void __clear_task_blocked_on(struct task_struct *p, struct m= utex *m) { - if (m) { - struct mutex *blocked_on =3D READ_ONCE(p->blocked_on); - - /* 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(blocked_on && blocked_on !=3D m); - } - WRITE_ONCE(p->blocked_on, NULL); + /* Currently we serialize blocked_on under the task::blocked_lock */ + lockdep_assert_held_once(&p->blocked_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; } =20 static inline void clear_task_blocked_on(struct task_struct *p, struct mut= ex *m) { - guard(raw_spinlock_irqsave)(&m->wait_lock); + guard(raw_spinlock_irqsave)(&p->blocked_lock); __clear_task_blocked_on(p, m); } #else diff --git a/init/init_task.c b/init/init_task.c index e557f622bd906..7e29d86153d9f 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -140,6 +140,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = =3D { .journal_info =3D NULL, INIT_CPU_TIMERS(init_task) .pi_lock =3D __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock), + .blocked_lock =3D __RAW_SPIN_LOCK_UNLOCKED(init_task.blocked_lock), .timer_slack_ns =3D 50000, /* 50 usec default slack */ .thread_pid =3D &init_struct_pid, .thread_node =3D LIST_HEAD_INIT(init_signals.thread_head), diff --git a/kernel/fork.c b/kernel/fork.c index c4ada32598bd5..796cfceb2bbda 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2030,6 +2030,7 @@ __latent_entropy struct task_struct *copy_process( ftrace_graph_init_task(p); =20 rt_mutex_init_task(p); + raw_spin_lock_init(&p->blocked_lock); =20 lockdep_assert_irqs_enabled(); #ifdef CONFIG_PROVE_LOCKING diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index 949103fd8e9b5..1d8cff71f65e1 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(__get_task_blocked_on(task)); + 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 __get_task_blocked_on(task); + 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 de7d6702cd96c..c44fc63d4476e 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -640,6 +640,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas goto err_early_kill; } =20 + raw_spin_lock(¤t->blocked_lock); __set_task_blocked_on(current, lock); set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); @@ -653,8 +654,9 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas * the handoff. */ if (__mutex_trylock(lock)) - goto acquired; + break; =20 + raw_spin_unlock(¤t->blocked_lock); /* * Check for signals and kill conditions while holding * wait_lock. This ensures the lock cancellation is ordered @@ -677,12 +679,14 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas =20 first =3D __mutex_waiter_is_first(lock, &waiter); =20 + raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); /* * 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 acquire. */ - set_task_blocked_on(current, lock); + __set_task_blocked_on(current, lock); set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -693,25 +697,33 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas break; =20 if (first) { - trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); + bool opt_acquired; + /* * mutex_optimistic_spin() can call schedule(), so - * clear blocked on so we don't become unselectable + * we need to release these locks before calling it, + * and 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)) + __clear_task_blocked_on(current, lock); + raw_spin_unlock(¤t->blocked_lock); + raw_spin_unlock_irqrestore(&lock->wait_lock, flags); + + trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); + opt_acquired =3D mutex_optimistic_spin(lock, ww_ctx, &waiter); + + raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); + __set_task_blocked_on(current, lock); + + if (opt_acquired) break; - set_task_blocked_on(current, lock); trace_contention_begin(lock, LCB_F_MUTEX); } - - raw_spin_lock_irqsave(&lock->wait_lock, flags); } - raw_spin_lock_irqsave(&lock->wait_lock, flags); -acquired: __clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); + raw_spin_unlock(¤t->blocked_lock); =20 if (ww_ctx) { /* @@ -740,11 +752,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas return 0; =20 err: - __clear_task_blocked_on(current, lock); + clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); __mutex_remove_waiter(lock, &waiter); err_early_kill: - WARN_ON(__get_task_blocked_on(current)); + 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); @@ -955,7 +967,7 @@ static noinline void __sched __mutex_unlock_slowpath(st= ruct mutex *lock, unsigne next =3D waiter->task; =20 debug_mutex_wake_waiter(lock, waiter); - __clear_task_blocked_on(next, lock); + 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 31a785afee6c0..e4a81790ea7dd 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -289,7 +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. */ - __clear_task_blocked_on(waiter->task, lock); + clear_task_blocked_on(waiter->task, lock); wake_q_add(wake_q, waiter->task); } =20 @@ -347,7 +347,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock, * are waking the mutex owner, who may be currently * blocked on a different mutex. */ - __clear_task_blocked_on(owner, NULL); + clear_task_blocked_on(owner, NULL); wake_q_add(wake_q, owner); } return true; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 631e25ce15c66..007459d42ae4a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6639,6 +6639,7 @@ static struct task_struct *proxy_deactivate(struct rq= *rq, struct task_struct *d * p->pi_lock * rq->lock * mutex->wait_lock + * p->blocked_lock * * Returns the task that is going to be used as execution context (the one * that is actually going to be run on cpu_of(rq)). @@ -6662,8 +6663,9 @@ find_proxy_task(struct rq *rq, struct task_struct *do= nor, struct rq_flags *rf) * and ensure @owner sticks around. */ guard(raw_spinlock)(&mutex->wait_lock); + guard(raw_spinlock)(&p->blocked_lock); =20 - /* Check again that p is blocked with wait_lock held */ + /* Check again that p is blocked with blocked_lock held */ if (mutex !=3D __get_task_blocked_on(p)) { /* * Something changed in the blocked_on chain and --=20 2.51.0.536.g15c5d4f767-goog