From nobody Sun Feb 8 15:32:23 2026 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 F330D244693 for ; Fri, 16 May 2025 03:18:27 +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=1747365509; cv=none; b=KD2erFkcD++MaDU6lpFpmHUBELV/vvRPeyPLd9X13VQpen9AZ7YG7rDEeRokaZYJEv0HdlH1LTPEY9nWUaf/VsWZWSwQdMJ6Rbks2zhLhpIFoTa+un6uafyZH0dWhFydrl+VLP9ikFJr+DeZo1KP2Y/X1kCsnDZ0tf27/dJFy8A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747365509; c=relaxed/simple; bh=J13+gjbzZcuWFW0zwgfTT1h9aoWFmVyRRxJG7aGbIg4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=F0NShEHbQF2tbvuoSGuSOEkpCegiaOCvbTV/Jng+xgAFMDLsqz4uxJ4XnIhlNtVExBJ4WibkVZz2o2QSZDzbKJV6YHZjacZyyX4+H1b1sVIW6XBexjNBdK11iHUtfSHL5mq0pcIzeTTuTtowQ3y2pHaQxrqoZpmCycWVaenzc68= 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=L/097j6D; 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="L/097j6D" Received: by mail-pf1-f202.google.com with SMTP id d2e1a72fcca58-73e0094706bso2154553b3a.3 for ; Thu, 15 May 2025 20:18:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1747365507; x=1747970307; 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=PeRbeyGeogzodH9RWPC+iqSgOIRx6ggwgE5/k1kRmQk=; b=L/097j6D1ITuov+yRESTtTCRnbh5qa8hHr4axinEjzo5XJU9kUzyvlzDyOpIvddLX7 0yRzT/hG9/CnZh/tSWMUL0dkQ1OJU1MdG5Y4rnVQa8mbSuyqSjYQN6i9O2zyHpJfh5/W e9Hb9Ui0G5Y2oX970FP/Bcjz1MzT2dQ+X1mTJ40sXrMr6cG/lED7dCa+5pQNXheczi/E lEkD57H3BHSIeR8Z2bAxT0xGL7jv+rABU6on1kjwA56WWsxEhpXx2B/Gqz8J+NnaTsHj p5aGGiSZzBXVNg3cAaBGBJRAgW2jiaEJyM+FIXQBwOi7rs9rGjpXZ/SgDvhU27sQVFoW gUVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1747365507; x=1747970307; 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=PeRbeyGeogzodH9RWPC+iqSgOIRx6ggwgE5/k1kRmQk=; b=e9YTSB6RtQZ8y7Au3lcdHyql0P3mth7QF4ENYu4IZEKRlYCN7kUCOiA0J8T1j99a83 x0JTkX7/N3Ny90Cc/LmzAM4NDyagXtoVlERMKx7l2X1BchS5p2mUhOf8fRVLCEbswhH8 QHGjHgFG44K9XBJtZ0bXPXfH+HqfAUfToALsl0JSGMSa5LfaiNrnl8xpSx8evkTv3sHB xLbtG9o1KxfTTMV8ba+aDo5nOm0+iJLw+v8PyGhDBrmupeCjz5clrv64pMGeQWvxVEre dnf7iSmGKL2uKs8rte8OhlOVS5UT55zkXXDUkW0QfA9tPyZJq9cifYC3SSOAVnhDGOHj k31A== X-Gm-Message-State: AOJu0YxXoAsQb7aiNhpwdc1lmBt+zDtxI4vBxtCuQjnBihmuBr8eEZuu 109UrTgoRRA45I/GcdnlQxyJ/oTDggwc0WcbvKKQ/TNSGG+lbGTRKYGTMe2XAbO0P9Mnp2drLxC htDBZ70g53vtT55x7G5pO9Y4Kr+7rz/5jfFaBTJKcJWtAh1UIHL8mUG6XKIOfif9ejVtKBhY3jc cLXXoo7GQpEDISO/Un181GR2bz/qaKM/0uCHbAsTFRtZU7i+kv X-Google-Smtp-Source: AGHT+IGQ4hpdp0+Si8Fc8LZ++YSMyAad1d4UnsN7jF/j07wRk+PWwxi/LVZjsW+1yJONWRVgCyNIcTbobPO2 X-Received: from pfrh4.prod.google.com ([2002:aa7:9f44:0:b0:742:aeb6:1b7a]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3a20:b0:732:a24:7354 with SMTP id d2e1a72fcca58-742a97a70d3mr2087097b3a.4.1747365507042; Thu, 15 May 2025 20:18:27 -0700 (PDT) Date: Fri, 16 May 2025 03:17:53 +0000 In-Reply-To: <20250516031814.1870508-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250516031814.1870508-1-jstultz@google.com> X-Mailer: git-send-email 2.49.0.1101.gccaa498523-goog Message-ID: <20250516031814.1870508-7-jstultz@google.com> Subject: [PATCH v17 6/8] sched: Add an initial sketch of the find_proxy_task() function From: John Stultz To: LKML Cc: 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" Add a find_proxy_task() function which doesn't do much. When we select a blocked task to run, we will just deactivate it and pick again. The exception being if it has become unblocked after find_proxy_task() was called. This allows us to validate keeping blocked tasks on the runqueue and later deactivating them is working ok, stressing the failure cases for when a proxy isn't found. Greatly simplified from patch by: Peter Zijlstra (Intel) Juri Lelli Valentin Schneider Connor O'Brien [jstultz: Split out from larger proxy patch and simplified for review and testing.] Signed-off-by: John Stultz --- v5: * Split out from larger proxy patch v7: * Fixed unused function arguments, spelling nits, and tweaks for clarity, pointed out by Metin Kaya * Fix build warning Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202311081028.yDLmCWgr-lkp@i= ntel.com/ v8: * Fixed case where we might return a blocked task from find_proxy_task() * Continued tweaks to handle avoiding returning blocked tasks v9: * Add zap_balance_callbacks helper to unwind balance_callbacks when we will re-call pick_next_task() again. * Add extra comment suggested by Metin * Typo fixes from Metin * Moved adding proxy_resched_idle earlier in the series, as suggested by Metin * Fix to call proxy_resched_idle() *prior* to deactivating next, to avoid crashes caused by stale references to next * s/PROXY/SCHED_PROXY_EXEC/ as suggested by Metin * Number of tweaks and cleanups suggested by Metin * Simplify proxy_deactivate as suggested by Metin v11: * Tweaks for earlier simplification in try_to_deactivate_task v13: * Rename rename "next" to "donor" in find_proxy_task() for clarity * Similarly use "donor" instead of next in proxy_deactivate * Refactor/simplify proxy_resched_idle * Moved up a needed fix from later in the series v15: * Tweaked some comments to better explain the initial sketch of find_proxy_task(), suggested by Qais * Build fixes for !CONFIG_SMP * Slight rework for blocked_on_state being added later in the series. * Move the zap_balance_callbacks to later in the patch series v16: * Move the enqueue_task_rt() out to later in the series, as suggested by K Prateek Nayak * Fixup whitespace error pointed out by K Prateek Nayak * Use put_prev_set_next_task as suggested by K Prateek Nayak * Try to rework find_proxy_task() locking to use guard and proxy_deactivate_task() in the way Peter suggested. v17: * Slightly simplified variable names per suggestion from Juri Lelli * Minor comment and commit message tweaks suggested by Peter 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 --- kernel/sched/core.c | 99 ++++++++++++++++++++++++++++++++++++++++++-- kernel/sched/sched.h | 10 ++++- 2 files changed, 105 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 82817650a635b..878d9c5fea53c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6600,7 +6600,7 @@ pick_next_task(struct rq *rq, struct task_struct *pre= v, struct rq_flags *rf) * Otherwise marks the task's __state as RUNNING */ static bool try_to_block_task(struct rq *rq, struct task_struct *p, - unsigned long task_state) + unsigned long task_state, bool deactivate_cond) { int flags =3D DEQUEUE_NOCLOCK; =20 @@ -6609,6 +6609,9 @@ static bool try_to_block_task(struct rq *rq, struct t= ask_struct *p, return false; } =20 + if (!deactivate_cond) + return false; + p->sched_contributes_to_load =3D (task_state & TASK_UNINTERRUPTIBLE) && !(task_state & TASK_NOLOAD) && @@ -6632,6 +6635,89 @@ static bool try_to_block_task(struct rq *rq, struct = task_struct *p, return true; } =20 +#ifdef CONFIG_SCHED_PROXY_EXEC +static inline struct task_struct *proxy_resched_idle(struct rq *rq) +{ + put_prev_set_next_task(rq, rq->donor, rq->idle); + rq_set_donor(rq, rq->idle); + set_tsk_need_resched(rq->idle); + return rq->idle; +} + +static bool __proxy_deactivate(struct rq *rq, struct task_struct *donor) +{ + unsigned long state =3D READ_ONCE(donor->__state); + + /* Don't deactivate if the state has been changed to TASK_RUNNING */ + if (state =3D=3D TASK_RUNNING) + return false; + /* + * Because we got donor from pick_next_task(), it is *crucial* + * that we call proxy_resched_idle() before we deactivate it. + * As once we deactivate donor, donor->on_rq is set to zero, + * which allows ttwu() to immediately try to wake the task on + * another rq. So we cannot use *any* references to donor + * after that point. So things like cfs_rq->curr or rq->donor + * need to be changed from next *before* we deactivate. + */ + proxy_resched_idle(rq); + return try_to_block_task(rq, donor, state, true); +} + +static struct task_struct *proxy_deactivate(struct rq *rq, struct task_str= uct *donor) +{ + if (!__proxy_deactivate(rq, donor)) { + /* + * XXX: For now, if deactivation failed, set donor + * as unblocked, as we aren't doing proxy-migrations + * yet (more logic will be needed then). + */ + donor->blocked_on =3D NULL; + } + return NULL; +} + +/* + * Initial simple sketch that just deactivates the blocked task + * chosen by pick_next_task() so we can then pick something that + * isn't blocked. + */ +static struct task_struct * +find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags = *rf) +{ + struct mutex *mutex; + + mutex =3D donor->blocked_on; + /* Something changed in the chain, so pick again */ + if (!mutex) + return NULL; + /* + * By taking mutex->wait_lock we hold off concurrent mutex_unlock() + * and ensure @owner sticks around. + */ + guard(raw_spinlock)(&mutex->wait_lock); + + /* Check again that donor is blocked with blocked_lock held */ + if (!task_is_blocked(donor) || mutex !=3D __get_task_blocked_on(donor)) { + /* + * Something changed in the blocked_on chain and + * we don't know if only at this level. So, let's + * just bail out completely and let __schedule() + * figure things out (pick_again loop). + */ + return NULL; /* do pick_next_task() again */ + } + return proxy_deactivate(rq, donor); +} +#else /* SCHED_PROXY_EXEC */ +static struct task_struct * +find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags = *rf) +{ + WARN_ONCE(1, "This should never be called in the !SCHED_PROXY_EXEC case\n= "); + return donor; +} +#endif /* SCHED_PROXY_EXEC */ + /* * __schedule() is the main scheduler function. * @@ -6742,12 +6828,19 @@ static void __sched notrace __schedule(int sched_mo= de) goto picked; } } else if (!preempt && prev_state) { - try_to_block_task(rq, prev, prev_state); + try_to_block_task(rq, prev, prev_state, + !task_is_blocked(prev)); switch_count =3D &prev->nvcsw; } =20 - next =3D pick_next_task(rq, prev, &rf); +pick_again: + next =3D pick_next_task(rq, rq->donor, &rf); rq_set_donor(rq, next); + if (unlikely(task_is_blocked(next))) { + next =3D find_proxy_task(rq, next, &rf); + if (!next) + goto pick_again; + } picked: clear_tsk_need_resched(prev); clear_preempt_need_resched(); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 154f0aa0c6322..ea2c987005bc1 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2264,6 +2264,14 @@ static inline int task_current_donor(struct rq *rq, = struct task_struct *p) return rq->donor =3D=3D p; } =20 +static inline bool task_is_blocked(struct task_struct *p) +{ + if (!sched_proxy_exec()) + return false; + + return !!p->blocked_on; +} + static inline int task_on_cpu(struct rq *rq, struct task_struct *p) { #ifdef CONFIG_SMP @@ -2473,7 +2481,7 @@ static inline void put_prev_set_next_task(struct rq *= rq, struct task_struct *prev, struct task_struct *next) { - WARN_ON_ONCE(rq->curr !=3D prev); + WARN_ON_ONCE(rq->donor !=3D prev); =20 __put_prev_set_next_dl_server(rq, prev, next); =20 --=20 2.49.0.1101.gccaa498523-goog