From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f202.google.com (mail-pf1-f202.google.com [209.85.210.202]) (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 999BC37C90D for ; Tue, 12 May 2026 02:56:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778554623; cv=none; b=Fy7/LY2cDYir0Qg7hjp4c/T8y5DJFbH3C0XPitw4FGt0RMS/+0m9SXicHKdm3VEy8O0ZKP4Ax+zF3Cmc77QoGYwHPJkG3WhmkZwV4mKucMlBbr0kXIEgJgmxBDbhOhndoakLOxIBazLYTbvsWCPWsZcSOQd73y1AOPGD7ueM+Fw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778554623; c=relaxed/simple; bh=SKueJJHIHNOunKZIsv5psY9ilW2Rwc5SI7MWOjSr2dE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ElStZie6ogjPZ6W4WH4ZiUVComs4NktDQPPbjgRwiLFQDf3C7//6D3oXYkdESK/PXdAuF/ytJLUjiRD0Bsi3tXm3tDfZ4Ej/jXwH/YpEDz8mc3wf6n8nKicZtRakHpdapRZVAT096cNPJozu2COMkKhKZMdZ0+Un+n8sO7shNMw= 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=E0OZvvpo; arc=none smtp.client-ip=209.85.210.202 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="E0OZvvpo" Received: by mail-pf1-f202.google.com with SMTP id d2e1a72fcca58-83ef22f8e8bso36332b3a.0 for ; Mon, 11 May 2026 19:56:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1778554610; x=1779159410; 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=76dfL95OPJNhHMWdWrMSyJO9GaVKGNAGD0FQczkg1GU=; b=E0OZvvpoMkXCU1Wc8YyEjDiQnULtLiePjR6MQAxrloZdjeVdQ3YBBfOk84YcnsFBUn jmLMZHM+U9c/f+8L5aqlnMrb32NlUC79Ctp2W3fmRFqAFOwIICFr6zwL+s6q58ymlJ00 UtptoWx2q4GOIIWgbyzWDaRlsetBxVOqgkFEeDaoWU2oPusCAoqacz5WLyAoSDUJhL0V 4RqGGOMpa+rYLXUmZXniy99Yju9k8Qts5/k9/nzP/0EfEFzDneZG3L1QPXSE1IeU6OIP ueZwfxPFiF7aZ3kupXlWu6qlj7DTWAQYmN+nGjgyMGBSFbHccOCagur2kYVTLzV+xRIP hnEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778554610; x=1779159410; 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=76dfL95OPJNhHMWdWrMSyJO9GaVKGNAGD0FQczkg1GU=; b=VtPQEWvb0whdi/OiKslSQ95KaKLS2Vvrq0CjoqcuFxCAhuz1CiAni1oPGmE6Bi0To6 3afX2kUWg+7mzB27KD/fmU86+2LAm9ocuSJOqe0Il00p5mfjLhYyOvBMRrlEFnHyeeB4 vIIvy3jfB3d5wUvbIMRigmGhfaDIFKBLEKdNl6qxzoQ2umd4s6GGZJjA0Lm7ObeV7x/A M79QrTA4VPxZWPmyJ0JKE4qmmMnGKLK4Bb/n6D+Del4BT/FzbaIX1EDAS1/jgwKTqMV/ b+dSfYnQRBaROZxW1W/SKR5yJyGJAYbuR3dk+9Mpxh/ILLLZBNW7JUdkBkkQBDgX/tvr 5uLQ== X-Gm-Message-State: AOJu0YyNjIAq3eDLaeoK1GnRDMiB8GBOH+4kdu49WPgIbpNCVHlVuU7B NbDhmT1Soh/CL1RrbErJxW6DjVllDsxVT3mpXT7bX2dH4s7F3nzzv+XkGBSg7MdbO+MFEdqS4y1 bkUkeAb4Tm0CnFuyFjb96FbsG18SPqqDRk6YGhBYpzAhcOi7lHtRG9iu9ifEcAxf5vc1FpMGqe/ t1+tLT/jbQdCt62Cwsf2lfHkLnDbRDp3NUjTwG5pmwXr2srrHO X-Received: from pfqp7.prod.google.com ([2002:aa7:9e87:0:b0:835:429c:76df]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:b484:b0:82a:7471:eb90 with SMTP id d2e1a72fcca58-83a5d0998bfmr26241507b3a.30.1778554609655; Mon, 11 May 2026 19:56:49 -0700 (PDT) Date: Tue, 12 May 2026 02:56:17 +0000 In-Reply-To: <20260512025635.2840817-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260512025635.2840817-1-jstultz@google.com> X-Mailer: git-send-email 2.54.0.563.g4f69b47b94-goog Message-ID: <20260512025635.2840817-8-jstultz@google.com> Subject: [PATCH v29 7/9] sched: Add blocked_donor link to task for smarter mutex handoffs From: John Stultz To: LKML Cc: Peter Zijlstra , Juri Lelli , Valentin Schneider , "Connor O'Brien" , John Stultz , Joel Fernandes , Qais Yousef , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Zimuzo Ezeozue , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kuyo chang , hupu , kernel-team@android.com Content-Type: text/plain; charset="UTF-8" From: Peter Zijlstra Add link to the task this task is proxying for, and use it so the mutex owner can do an intelligent hand-off of the mutex to the task that the owner is running on behalf. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Juri Lelli Signed-off-by: Valentin Schneider Signed-off-by: Connor O'Brien [jstultz: This patch was split out from larger proxy patch] Signed-off-by: John Stultz --- v5: * Split out from larger proxy patch v6: * Moved proxied value from earlier patch to this one where it is actually used * Rework logic to check sched_proxy_exec() instead of using ifdefs * Moved comment change to this patch where it makes sense v7: * Use more descriptive term then "us" in comments, as suggested by Metin Kaya. * Minor typo fixup from Metin Kaya * Reworked proxied variable to prev_not_proxied to simplify usage v8: * Use helper for donor blocked_on_state transition v9: * Re-add mutex lock handoff in the unlock path, but only when we have a blocked donor * Slight reword of commit message suggested by Metin v18: * Add task_init initialization for blocked_donor, suggested by Suleiman v23: * Reworks for PROXY_WAKING approach suggested by PeterZ v25: * Simplified some logic now we don't have proxy_tag_curr() v28: * Remove sched_proxy_exec() conditionalized blocked_lock usage as it was hitting llvm's "'blocked_lock' is not held on every path through here [-Wthread-safety-analysis]" errors. 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: 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 | 1 + init/init_task.c | 1 + kernel/fork.c | 1 + kernel/locking/mutex.c | 43 +++++++++++++++++++++++++++++++++++++++--- kernel/sched/core.c | 14 +++++++++++++- 5 files changed, 56 insertions(+), 4 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index bbb183233855a..c93883ce82ee4 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1242,6 +1242,7 @@ struct task_struct { #endif struct mutex *blocked_on; /* lock we're blocked on */ + struct task_struct *blocked_donor; /* task that is boosting this task */ raw_spinlock_t blocked_lock; #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER diff --git a/init/init_task.c b/init/init_task.c index b5f48ebdc2b6e..41c19670c8f6b 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -200,6 +200,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = { .mems_allowed_seq = SEQCNT_SPINLOCK_ZERO(init_task.mems_allowed_seq, &init_task.alloc_lock), #endif + .blocked_donor = NULL, #ifdef CONFIG_RT_MUTEXES .pi_waiters = RB_ROOT_CACHED, .pi_top_task = NULL, diff --git a/kernel/fork.c b/kernel/fork.c index 5f3fdfdb14c7c..7e50e42ec4d97 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2218,6 +2218,7 @@ __latent_entropy struct task_struct *copy_process( lockdep_init_task(p); p->blocked_on = NULL; /* not blocked yet */ + p->blocked_donor = NULL; /* nobody is boosting p yet */ #ifdef CONFIG_BCACHE p->sequential_io = 0; diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 09534628dc01a..0064b724ccda3 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -980,7 +980,7 @@ EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible); static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip) __releases(lock) { - struct task_struct *next = NULL; + struct task_struct *donor, *next = NULL; struct mutex_waiter *waiter; DEFINE_WAKE_Q(wake_q); unsigned long owner; @@ -1001,6 +1001,12 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne MUTEX_WARN_ON(__owner_task(owner) != current); MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP); + if (sched_proxy_exec() && current->blocked_donor) { + /* force handoff if we have a blocked_donor */ + owner = MUTEX_FLAG_HANDOFF; + break; + } + if (owner & MUTEX_FLAG_HANDOFF) break; @@ -1013,19 +1019,50 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne } raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); debug_mutex_unlock(lock); + + if (sched_proxy_exec()) { + /* + * If we have a task boosting current, and that task was boosting + * current through this lock, hand the lock to that task, as that + * is the highest waiter, as selected by the scheduling function. + */ + donor = current->blocked_donor; + if (donor) { + struct mutex *next_lock; + + raw_spin_lock_nested(&donor->blocked_lock, SINGLE_DEPTH_NESTING); + next_lock = __get_task_blocked_on(donor); + if (next_lock == lock) { + next = donor; + __set_task_blocked_on_waking(donor, next_lock); + wake_q_add(&wake_q, donor); + current->blocked_donor = NULL; + } + raw_spin_unlock(&donor->blocked_lock); + } + } + + /* + * Failing that, pick first on the wait list. + */ waiter = lock->first_waiter; - if (waiter) { + if (!next && waiter) { next = waiter->task; + raw_spin_lock_nested(&next->blocked_lock, SINGLE_DEPTH_NESTING); debug_mutex_wake_waiter(lock, waiter); - set_task_blocked_on_waking(next, lock); + __set_task_blocked_on_waking(next, lock); + raw_spin_unlock(&next->blocked_lock); wake_q_add(&wake_q, next); + } if (owner & MUTEX_FLAG_HANDOFF) __mutex_handoff(lock, next); + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q); } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8a223555be2e9..2226f594376d6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6821,7 +6821,17 @@ static void proxy_migrate_task(struct rq *rq, struct rq_flags *rf, * Find runnable lock owner to proxy for mutex blocked donor * * Follow the blocked-on relation: - * task->blocked_on -> mutex->owner -> task... + * + * ,-> task + * | | blocked-on + * | v + * blocked_donor | mutex + * | | owner + * | v + * `-- task + * + * and set the blocked_donor relation, this latter is used by the mutex + * code to find which (blocked) task to hand-off to. * * Lock order: * @@ -6963,6 +6973,7 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf) * rq, therefore holding @rq->lock is sufficient to * guarantee its existence, as per ttwu_remote(). */ + owner->blocked_donor = p; } WARN_ON_ONCE(owner && !owner->on_rq); return owner; @@ -7119,6 +7130,7 @@ static void __sched notrace __schedule(int sched_mode) clear_task_blocked_on(prev, NULL); rq_set_donor(rq, next); + next->blocked_donor = NULL; if (unlikely(next->is_blocked && next->blocked_on)) { next = find_proxy_task(rq, next, &rf); if (!next) { -- 2.54.0.563.g4f69b47b94-goog