From nobody Sun Jun 14 15:53:28 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5B40D3932DB; Fri, 3 Apr 2026 12:30:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775219429; cv=none; b=KKpWvPqyMYCmqUiXH32LRG9MBAXiWpiD0vPJey9zcGKvHIAhVKQsrT0pwkRv+LVPyLUD1zLQSp2EbR2NGmTCSi+9FvIbCgTWTpi2dzQI3mg251DzCqeiHR/SZPuikjquArsB1WXMm1QWb3nRdl4ahWvZU+MPGtXQRGGgpuOGf1Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775219429; c=relaxed/simple; bh=KTuBHvTGAUsADJ5mA9OREZVLJwlD5jhfcN4gvRlMp+k=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=jtiY7PGgW6uES0XaGU7/uSjWPZJ+LMatxL/HFI7/K6Scpuk6miG71OhheDJSFkCDiB0ceUC9zK4breNKxBpSACwDuagqshHJeRv4Rq7olvn5CRKDv/bqezM13l9ULShR/RTN2Xvg+2+vDHgNAG6kMllhrN+86ITitWlIBVcLZ4I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=fxXVqyVO; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=uvqu7/Jz; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="fxXVqyVO"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="uvqu7/Jz" Date: Fri, 03 Apr 2026 12:30:24 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1775219425; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sd9q2M8DdCSugwRTz3JWZFax+ZrrTUrxGuOjytVM/4Q=; b=fxXVqyVOp2cLppZbRPpPKPo6g7OBd6wcwQmKQ30S5kgj/Y0aoxvVy3gKLWcnfIdGU+D2Jb miG0WKrp+BplOBBBHhpzkQF1z7LIdDhCNDi2xF9mC7gmCBY4gbk4EVJDuoPzH3bj+44rZI cYVXwtdIyaNtvR7X58YvyGujUdgKbSHC2/rtar0n2b4dMKGcxlvgSLy+PDz6TwP6o/g8z6 G1uDcY+Uake8Xbj/FcKF/nknNvo7m2sVlSU9ZypGHqgD/ukaJ5+nTeycy7QwYpBwoDBZdD +zUjnOYBFzvKr4BcgmemyydSV5E0lVCSCxSVfGMmmOxHbRlu2Zx4ub2lSqyDVw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1775219425; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sd9q2M8DdCSugwRTz3JWZFax+ZrrTUrxGuOjytVM/4Q=; b=uvqu7/Jzl0vP5fCmHl5dxGPKXYzwLQ4Ll5/ZOVVqGb1LbwQLV7kuow27aw71zLfRQQ2Dv0 kzc/h5E+Ou6xMeCQ== From: "tip-bot2 for John Stultz" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] locking: Add task::blocked_lock to serialize blocked_on state Cc: John Stultz , "Peter Zijlstra (Intel)" , K Prateek Nayak , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20260324191337.1841376-5-jstultz@google.com> References: <20260324191337.1841376-5-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <177521942464.1647592.3000438941695378587.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the sched/core branch of tip: Commit-ID: fa4a1ff8ab235a308d8c983827657a69649185fd Gitweb: https://git.kernel.org/tip/fa4a1ff8ab235a308d8c983827657a696= 49185fd Author: John Stultz AuthorDate: Tue, 24 Mar 2026 19:13:19=20 Committer: Peter Zijlstra CommitterDate: Fri, 03 Apr 2026 14:23:39 +02:00 locking: Add task::blocked_lock to serialize blocked_on state 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: K Prateek Nayak Link: https://patch.msgid.link/20260324191337.1841376-5-jstultz@google.com --- include/linux/sched.h | 48 ++++++++++++----------------------- init/init_task.c | 1 +- kernel/fork.c | 1 +- kernel/locking/mutex-debug.c | 4 +-- kernel/locking/mutex.c | 40 ++++++++++++++++++----------- kernel/locking/mutex.h | 6 ++++- kernel/locking/ww_mutex.h | 4 +-- kernel/sched/core.c | 4 ++- 8 files changed, 58 insertions(+), 50 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 5a5d3db..2eef9bc 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1238,6 +1238,7 @@ 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 /* @@ -2181,57 +2182,42 @@ extern int __cond_resched_rwlock_write(rwlock_t *lo= ck) __must_hold(lock); #ifndef CONFIG_PREEMPT_RT 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; + lockdep_assert_held_once(&p->blocked_lock); + return p->blocked_on; } =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 5c83875..b5f48eb 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -169,6 +169,7 @@ 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 bc2bf58..079802c 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2076,6 +2076,7 @@ __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 2c6b02d..cc6aa9c 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 2a1d165..4aa79bc 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -656,6 +656,7 @@ __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); @@ -669,8 +670,9 @@ __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 @@ -693,12 +695,14 @@ __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 @@ -709,25 +713,33 @@ __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) { /* @@ -756,11 +768,11 @@ skip_wait: 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); @@ -971,7 +983,7 @@ 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/mutex.h b/kernel/locking/mutex.h index 9ad4da8..7a8ba13 100644 --- a/kernel/locking/mutex.h +++ b/kernel/locking/mutex.h @@ -47,6 +47,12 @@ static inline struct task_struct *__mutex_owner(struct m= utex *lock) return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLA= GS); } =20 +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); +} + #ifdef CONFIG_DEBUG_MUTEXES extern void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter); diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 31a785a..e4a8179 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 5b7f378..1913dbc 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6584,6 +6584,7 @@ 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)). @@ -6603,8 +6604,9 @@ 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