From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 48057383C97 for ; Wed, 22 Apr 2026 23:07:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776899240; cv=none; b=TRl5RJSpCjuf5lrmAWoLZBd0u25ogoBx3jzjXzVoaL1G15d2p+BQYKExubSxBiTYFyDuzHs4keoSN1DBOtKyVQt8iSlS8DaWUBjDt3H+Vvm28qv4cFO696FSJ04MGBSSSHy8gytlbnA8x+MN5xWA6ixn6mNWETPHnajD5EUMi8E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776899240; c=relaxed/simple; bh=zLAWmC8SEilSP2upfSM5Xp7xMO6OSj1mdldNAqGQMs4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=jbA9PRNfvR3Tkf2vGtALXwIUwTEizO4bthKiIjrFAQKclJ35IjayyMoaaqUVMXUa262AtjKXus7rHSfxUftBB7cRxWrpjPsIUXJXo4aYVhAjSUfUaah8le5Ccs6C+TYXmoRHxgufms/3X2ckmbvGaalNbov1acAgMEw1mqc1xXI= 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=TgU+Rl5F; arc=none smtp.client-ip=209.85.216.73 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="TgU+Rl5F" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-358f058973fso7422109a91.1 for ; Wed, 22 Apr 2026 16:07:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1776899236; x=1777504036; 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=1lvtAoImYg+N2TMW1qJHwAlCROLzg7IxwF+Mm2urAgQ=; b=TgU+Rl5FoqhDlv2WXEFn3uQOys3kXUeg0WcZjmrn+YDOT7DwuwDrUN2Cr7l3ZnaMRu ruhM8LFUbwnocbBN/pfFsaCnebtjLnxymFBEdxQIDN6Kidc518C6OsmQU0NtcLGCGNjf Hv6kmygamT7OgqKthrEeoUDAJCyEVfQbW1ekQ/D7tntzu5Q16nfho8lTDD3wF05UzJ/4 7twRyHiOrzy4xK/eJzbpQ+dq8/v1iFi7soECnS2wrlbgykdsWTmzW8cl0cd8c3aRu+Cq sHdP+DNm5mJsr3BQhBNujldNAmFqN1MeBNKPYxtzTtCk90lj34kDi/jPX27zxouMcUB+ qdEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776899236; x=1777504036; 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=1lvtAoImYg+N2TMW1qJHwAlCROLzg7IxwF+Mm2urAgQ=; b=FUX+2AyXGceUsauL8E62bSl640yu82iBqPsK32UvIyat6qg5gy545GSO5gJJ4ctNIU 39c41OtnXKANCF2j47MhE4c/+aRWWiETiGbTWPnCc4uABLocbxMbbhM5XvkjtLQIzOhI agX0gKmsM8simXLrxqpUZNY7y7rkTTExF8r+Y4GLACXrzi7X8SMGO4oCoa4x1E+Ie0l1 KlDd1Jt8tkFdZq/+ulPSJcvMhYGyI6r87xSb0TKQlh7XFVoBDs/kw+FarDBPFLBj1gKv TvcAkUbGErNmum+huX4R/weXQGidiCZ3JX301QyvMQjkHlxjnSUwifk6mc2VSDyuCa1J JGCA== X-Gm-Message-State: AOJu0Yy/8e1chFmFspKTaSD+9kbBjD8bZI3qBH6tOf/5H284DJ+HX8L3 PYKZtHFByRuO5Q0Gw6i8nT4ErhfeCMBfrS7Pp6WuBmpSZrj1CupOojTrAgPtydF4Sqyfw6FraYg 8Z3xuww9T7fht27AIJYF4pyQdC2kU087jC5S0ZmozFaCagUkVNUys+vmVlCtyuHbkez9cH4FRfN o7W3fWksYkpnJdup/ve44KMM0uo6Q8zONzyt30r1vzh0OYhe0w X-Received: from pjbmj17.prod.google.com ([2002:a17:90b:3691:b0:35d:a01d:80ab]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4cca:b0:35d:93ff:2854 with SMTP id 98e67ed59e1d1-361403f1311mr24521039a91.8.1776899235402; Wed, 22 Apr 2026 16:07:15 -0700 (PDT) Date: Wed, 22 Apr 2026 23:06:47 +0000 In-Reply-To: <20260422230659.903191-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260422230659.903191-1-jstultz@google.com> X-Mailer: git-send-email 2.54.0.rc2.533.g4f5dca5207-goog Message-ID: <20260422230659.903191-7-jstultz@google.com> Subject: [PATCH v28 6/8] 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 Fixup for llvm 'blocked_lock' is not held on every path through here [-Wthread-safety-analysis] Clang is fussy so lets not do conditional locking --- 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 5b68a1c9eedcf..65791d7359553 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1239,6 +1239,7 @@ 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 f1ad69c6dc2d4..c1d65b86729d6 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2216,6 +2216,7 @@ __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 6e6699d9fcba6..333f33d33ef06 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -976,7 +976,7 @@ 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; @@ -997,6 +997,12 @@ 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; @@ -1009,19 +1015,50 @@ 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 17797e1f76f25..edd418dde1e47 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6809,7 +6809,17 @@ 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: * @@ -6949,6 +6959,7 @@ 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; @@ -7105,6 +7116,7 @@ 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->blocked_on)) { next = find_proxy_task(rq, next, &rf); if (!next) { -- 2.54.0.rc2.533.g4f5dca5207-goog