From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 F27D133506C for ; Sat, 4 Apr 2026 05:36:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775281010; cv=none; b=DucF5pBb03KF2X5wNYe13zjczkoQTKOGV1d3trAQzNGlv4NUP3rIrSDtWsm+jn0GYNYe87PggFklDgbMggJcCAXhY3YrgCLHQxNSTM+y5FiEl0SjG2BDJOcWAs5XG86LPQpZzrvtco+WAT5viAagBogZvsSDKfWQmBp3VPMmxe8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775281010; c=relaxed/simple; bh=pTSPEL6AHZdvVxI/gJ2g16EBrOQoIsK9A3Ps2Ju1JXA=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=pvz/5yyenvepcaanrwKSoe1Yd0Jh80Drm0DTjKMFRD89IMoW40wA5IVDX0keMqEcGyJtSQhMTD1f3aHWef4QcwJOxwQKmSR96x9fAy5eGP9XwBNAx1+UQm6Voa+fNZ2waqJlpeoan25mbdZqjEDNUuv1Geq7BvUorJo/4z+WvP0= 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=fz9qlngs; arc=none smtp.client-ip=209.85.214.201 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="fz9qlngs" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-2b0f4e632caso35326455ad.3 for ; Fri, 03 Apr 2026 22:36:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775281008; x=1775885808; 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=Ztbl+3T3jxHP87PGN7Exc4Dus6q/0xepccEC4U2P7C0=; b=fz9qlngswH2kFPETe10CtSfiAQ+tuRFZu7q5/ZzfQU13Tkcu6ngYNAram9YSiRc578 zECS87P0ZCecEuSfNxq6Xqvlh3ULMU+vjOCiq9qZ7Wk7TvuwpD+5B48eRuY/oM8hmH2C 6lkU/9YDR3ygus0JjdfeYaobyJi/XCEFA3mBosRQATFUeyEP65FmYMI2apaA+SBpzn1K fJCwRvJlvhD8jZO4hi72kL6HWAI2np5HfeY7b37z0cc9I9bX7vBWfIT3csd3w84fp0/e Ai/GzLknIBDiAk1ZSOX2+lcZ6rbc71rb15lp92SvhLpQnkdmj0RHsf/E8XU3rZz1T9C/ d0nw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775281008; x=1775885808; 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=Ztbl+3T3jxHP87PGN7Exc4Dus6q/0xepccEC4U2P7C0=; b=bmwNc2R7ODLWYg68ZhDIMUirzbEBWOc5PxMt/wqmXDHTbaCgeujU5p2RlAd4bPFhvy UZDgzY4Jhe8mwfJDdFI1H/zC/XCVbr8EArdONv6CvgkZtgPTPjey3uEFEIv5/+2udJYo sRhskd5AQdgmWqpdQeEbLy8v4Pua43+gR6PvYRksdGwBpmaCe/4Ojo0qfKY2jwUEg+vR ORNPJnbsqegoiUvhM5lucnEh1ryIcaeXu+r+dh6ccB/csRo+qFGwBnxi5ggnXk+7S0BL F9Z4G3u8vCiu8AB0aZ2yIeLUB/pJ0II2v8q94CQ5tzcXgXPL4cYCNk1hO2ENjfA6SZ1Z LH1Q== X-Gm-Message-State: AOJu0Yx8ecddXUcJZhthl8ukT72+nsdc+baBkufDWvmuaKUMwVolmEwg FCKNBE27f446OSkXxMSQ8JD9+18fiMHzsOKmpXDaOEuB+IP+rEKMoYgoR+rq4RELpTlhA0Gq5Nc K4v3ZAp+EL7qq1iRZd+FDtkBeYy4w8vmEQOVr52IZPnRc/rYhD40l0gIypT/Ugl4uYrNYlGKqoV oyR6Jy6TUTjL+HEfayxAhiEv4Pv77bjhBmLRccuZ87USMdSJPl X-Received: from pgib11.prod.google.com ([2002:a63:e70b:0:b0:c6e:4b29:e099]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:3396:b0:398:aea8:a9c0 with SMTP id adf61e73a8af0-39f2eff034amr5328612637.19.1775281006636; Fri, 03 Apr 2026 22:36:46 -0700 (PDT) Date: Sat, 4 Apr 2026 05:36:21 +0000 In-Reply-To: <20260404053632.1729280-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260404053632.1729280-1-jstultz@google.com> X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <20260404053632.1729280-5-jstultz@google.com> Subject: [PATCH v27 04/10] sched: deadline: Add dl_rq->curr pointer to address issues with Proxy Exec From: John Stultz To: LKML Cc: John Stultz , Peter Zijlstra , Joel Fernandes , Qais Yousef , Ingo Molnar , 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-Type: text/plain; charset="UTF-8" The DL scheduler keeps the current task in the rbtree, since the deadline value isn't usually chagned while the task is runnable. This results in set_next_task() and put_prev_task() being simpler, but unfortunately this causes complexity elsewhere. Specifically when update_curr_dl() updates the deadline, it has to dequeue and then enqueue the task. >From put_prev_task_dl(), we first call update_curr_dl(), and then call enqueue_pushable_dl_task(). However, with Proxy Exec this goes awry. Since when a mutex is released, we might wake the waiting rq->donor. This will cause put_prev_task() to be called on the donor to take it off the cpu for return migration. At that point, from put_prev_task_dl() the update_curr_dl() logic will dequeue & enqueue the task, and the enqueue function will call enqueue_pushable_dl_task() (since the task_current() check won't prevent it). Then back up the callstack in put_prev_task_dl() we'll end up calling enqueue_pushable_dl_task() again, tripping the !RB_EMPTY_NODE(&p->pushable_dl_tasks) warning. So to avoid this, use Peter's suggested[1] approach, and add a dl_rq->curr pointer that is set/cleared from set_next_task()/ put_prev_task(), which effectively tracks the rq->donor. We can then use this to avoid adding the active donor to the pushable list from enqueue_task_dl(). [1]: https://lore.kernel.org/lkml/20260304095123.GP606826@noisy.programming.kicks-ass.net/ Suggested-by: Peter Zijlstra Signed-off-by: John Stultz --- 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/deadline.c | 13 +++++++++++++ kernel/sched/sched.h | 1 + 2 files changed, 14 insertions(+) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 60ccb492c4427..3ba5f8deb3687 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2352,6 +2352,9 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags) if (task_is_blocked(p)) return; + if (dl_rq->curr == dl_se) + return; + if (!task_current(rq, p) && !p->dl.dl_throttled && p->nr_cpus_allowed > 1) enqueue_pushable_dl_task(rq, p); } @@ -2574,6 +2577,10 @@ static void start_hrtick_dl(struct rq *rq, struct sched_dl_entity *dl_se) } #endif /* !CONFIG_SCHED_HRTICK */ +/* + * DL keeps current in tree, because ->deadline is not typically changed while + * a task is runnable. + */ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first) { struct sched_dl_entity *dl_se = &p->dl; @@ -2586,6 +2593,9 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first) /* You can't push away the running task */ dequeue_pushable_dl_task(rq, p); + WARN_ON_ONCE(dl_rq->curr); + dl_rq->curr = dl_se; + if (!first) return; @@ -2656,6 +2666,9 @@ static void put_prev_task_dl(struct rq *rq, struct task_struct *p, struct task_s update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 1); + WARN_ON_ONCE(dl_rq->curr != dl_se); + dl_rq->curr = NULL; + if (task_is_blocked(p)) return; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 8ee82b03a8a10..adefea777e0a5 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -880,6 +880,7 @@ struct dl_rq { bool overloaded; + struct sched_dl_entity *curr; /* * Tasks on this rq that can be pushed away. They are kept in * an rb-tree, ordered by tasks' deadlines, with caching -- 2.53.0.1213.gd9a14994de-goog