From nobody Thu Oct 2 00:49:10 2025 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 67698265CA8 for ; Fri, 26 Sep 2025 03:29:41 +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=1758857383; cv=none; b=CGlG//0E/7tAB7P/IFdD8xW4ZM7Q+G9iABFAeiObhMIiAVXW+zznDHAkj7piZ5YM5RVayC27ud4MfGLHFgfEzTFTCViSsN2PNP6l28TovKy7UlOUXASM02eakqAl9NehOaxJXgk7FP6rDsbByqyVLDNhxqyi0S9DyUgmdwGJCvQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857383; c=relaxed/simple; bh=ByK8/x1tt5oPdvHfzNUqnZZefft3Yw5ZeiFyCsyeXdo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=eSFWH3SYOB6LeUcuBJ9O2qfETVQO/zS5lVeeuDUohNv8RA50IksPRnjGgIEfJWZoZ5lt2D9tsgicb5pc5rXs5vyF3KbW1EfRbnXIWa9X2N3dPiXp7pSIWmQtI1y82ZdPdqTPjbblDvDIgZpj6zrvKlLmmC0Osj3fnKqzh9ZTMXk= 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=cxxeJR5J; 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="cxxeJR5J" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-32eb18b5500so2908092a91.2 for ; Thu, 25 Sep 2025 20:29:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1758857381; x=1759462181; 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=EjwZVObXSdDQzqr9JPtk/bu6D9iQBNEIElU8HnQUaaI=; b=cxxeJR5JaHGXFuC0GKaMboejRVNpbhirqVPUwNFY8aVrwYcvQQ1DzcrUpYKrJ/MEYY P1ps8U8Ojjp2C5mT8fmYYtygnHaUjvCR3/yx47dmfaInbdd32ARklJV11eO8K9AdOg3c zfh2XSjUlWY0BgrFqmSNtg/QFB5N4itlHS5XiPwfWGSN4jWHnyaJvGVd4RAzUHdm2E2u dnoVdCmfmoTe4mCkrUKM8xPmdgQaMg0AnKWatfsRRmwZQHKtwQnNNL+sS8Z0p9kk9in8 yLvYhHS4oKjl58OLhNZGNlvGZrUSvhaQ2vrr+fGIyJ4APQGcP+uTXvylUpSghG535dZo N3Zw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758857381; x=1759462181; 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=EjwZVObXSdDQzqr9JPtk/bu6D9iQBNEIElU8HnQUaaI=; b=Tv9d0NT1Y9aP6uzmIJ+1PwVNcY6rgBaAukJxgIy3zD0N+ptcAYEWXP4E++6srB77TA sjI1nNTa+Lxb04StPsvWeuy2/o5Hi9Y8NN4HIX6NqrKbohpvgzWpdDl4EbDwaJZRsVj5 t8ZV5wrOCZH2WVWxVxEKOwPYpoKc4ih4PqcqdEywyOgqgYBdUxvVeQV1ou20pZBE6A4b 1iUs9ihSAKEZs1nm2MwI4KXxF/FObYTiJ5HmNXfIIMaUAfUmDBqkAtiQzE/76eu0aBTH 33bvScRvWf6dJV+EFyv3Z9/xuT9hznYGNhQck7kx0Lg1s+OMqs7SqdzLFklY2flK+ueK hc+A== X-Gm-Message-State: AOJu0YxtIe9+QfChnpdqWm1eceJ3e+1Y5HEJJyOmc7/HLQnstnV1pC6C SH9uZ5pGKB0lhkLMZQFLyNtATRlyZcY02NEXrM5cO59IEVoL1C7R9NLjB6iRTPoW5I7vhhjIKWP oiyBQZKvDrWZMYiwEocCMDAI/dq+iSY220yUBME2wz0eejn4DEkqmyJe7zgx9aCYfEePeEqsMdg g2GDcZJoLCmJ/AkA6PHY9MHWzvDa5gQuHPFHvz5iY4ScyXCW1/ X-Google-Smtp-Source: AGHT+IHQHfHAJOJ99kyAbp3SU+NAOR0hzqg9heJZeiVkns8I+waWarOs6Ql+bJRJqop8tMiOydECBznl/i5b X-Received: from pjbmi6.prod.google.com ([2002:a17:90b:4b46:b0:330:793a:2e77]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:380f:b0:32e:32e4:9789 with SMTP id 98e67ed59e1d1-3342a257486mr6517076a91.3.1758857380535; Thu, 25 Sep 2025 20:29:40 -0700 (PDT) Date: Fri, 26 Sep 2025 03:29:11 +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: <20250926032931.27663-4-jstultz@google.com> Subject: [PATCH v22 3/6] sched: Add logic to zap balance callbacks if we pick again 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 , kuyo chang , hupu , kernel-team@android.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" With proxy-exec, a task is selected to run via pick_next_task(), and then if it is a mutex blocked task, we call find_proxy_task() to find a runnable owner. If the runnable owner is on another cpu, we will need to migrate the selected donor task away, after which we will pick_again can call pick_next_task() to choose something else. However, in the first call to pick_next_task(), we may have had a balance_callback setup by the class scheduler. After we pick again, its possible pick_next_task_fair() will be called which calls sched_balance_newidle() and sched_balance_rq(). This will throw a warning: [ 8.796467] rq->balance_callback && rq->balance_callback !=3D &balance_p= ush_callback [ 8.796467] WARNING: CPU: 32 PID: 458 at kernel/sched/sched.h:1750 sched= _balance_rq+0xe92/0x1250 ... [ 8.796467] Call Trace: [ 8.796467] [ 8.796467] ? __warn.cold+0xb2/0x14e [ 8.796467] ? sched_balance_rq+0xe92/0x1250 [ 8.796467] ? report_bug+0x107/0x1a0 [ 8.796467] ? handle_bug+0x54/0x90 [ 8.796467] ? exc_invalid_op+0x17/0x70 [ 8.796467] ? asm_exc_invalid_op+0x1a/0x20 [ 8.796467] ? sched_balance_rq+0xe92/0x1250 [ 8.796467] sched_balance_newidle+0x295/0x820 [ 8.796467] pick_next_task_fair+0x51/0x3f0 [ 8.796467] __schedule+0x23a/0x14b0 [ 8.796467] ? lock_release+0x16d/0x2e0 [ 8.796467] schedule+0x3d/0x150 [ 8.796467] worker_thread+0xb5/0x350 [ 8.796467] ? __pfx_worker_thread+0x10/0x10 [ 8.796467] kthread+0xee/0x120 [ 8.796467] ? __pfx_kthread+0x10/0x10 [ 8.796467] ret_from_fork+0x31/0x50 [ 8.796467] ? __pfx_kthread+0x10/0x10 [ 8.796467] ret_from_fork_asm+0x1a/0x30 [ 8.796467] This is because if a RT task was originally picked, it will setup the rq->balance_callback with push_rt_tasks() via set_next_task_rt(). Once the task is migrated away and we pick again, we haven't processed any balance callbacks, so rq->balance_callback is not in the same state as it was the first time pick_next_task was called. To handle this, add a zap_balance_callbacks() helper function which cleans up the balance callbacks without running them. This should be ok, as we are effectively undoing the state set in the first call to pick_next_task(), and when we pick again, the new callback can be configured for the donor task actually selected. Signed-off-by: John Stultz --- v20: * Tweaked to avoid build issues with different configs v22: * Spelling fix suggested by K Prateek * Collapsed the stub implementation to one line as suggested by K Prateek * Zap callbacks when we resched idle, as 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 --- kernel/sched/core.c | 41 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 39 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index abecd2411e29e..7bba05c07a79d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5001,6 +5001,38 @@ static inline void finish_task(struct task_struct *p= rev) smp_store_release(&prev->on_cpu, 0); } =20 +#ifdef CONFIG_SCHED_PROXY_EXEC +/* + * Only called from __schedule context + * + * There are some cases where we are going to re-do the action + * that added the balance callbacks. We may not be in a state + * where we can run them, so just zap them so they can be + * properly re-added on the next time around. This is similar + * handling to running the callbacks, except we just don't call + * them. + */ +static void zap_balance_callbacks(struct rq *rq) +{ + struct balance_callback *next, *head; + bool found =3D false; + + lockdep_assert_rq_held(rq); + + head =3D rq->balance_callback; + while (head) { + if (head =3D=3D &balance_push_callback) + found =3D true; + next =3D head->next; + head->next =3D NULL; + head =3D next; + } + rq->balance_callback =3D found ? &balance_push_callback : NULL; +} +#else +static inline void zap_balance_callbacks(struct rq *rq) {} +#endif + static void do_balance_callbacks(struct rq *rq, struct balance_callback *h= ead) { void (*func)(struct rq *rq); @@ -6942,10 +6974,15 @@ static void __sched notrace __schedule(int sched_mo= de) rq_set_donor(rq, next); if (unlikely(task_is_blocked(next))) { next =3D find_proxy_task(rq, next, &rf); - if (!next) + if (!next) { + /* zap the balance_callbacks before picking again */ + zap_balance_callbacks(rq); goto pick_again; - if (next =3D=3D rq->idle) + } + if (next =3D=3D rq->idle) { + zap_balance_callbacks(rq); goto keep_resched; + } } picked: clear_tsk_need_resched(prev); --=20 2.51.0.536.g15c5d4f767-goog