From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0D7CA1DE2BE; Wed, 19 Feb 2025 08:56:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739955385; cv=none; b=m/vTcS+OaSpnCZ2mP6L+acKJBeYx9LpwWW8fJbUwKiUJBDVo2IufBDBIRCBiHrtDYC+C1LzkxORdrUxN5+67R0NDclJegwCcrhfxf5c98pBXCjLjPGJWzum6YkRjXXxZN8hZwWoeSUp1lo5ij/3JaixjWHLFWSgoj/rpfBNO5PU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739955385; c=relaxed/simple; bh=z4canbL1ccqsuvByLkRhTKXn0wz7D9F/HLO7C0DutrY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=C8UXgXAKQb5VJ/SciGxS+3o5VBNvibByMvZFtqgvPR2pZOu5MyBprEAIFCnkn21LCAlws2MJVkMT23Epuofek0/5Bd5x84+KmNMmf7T6TfVHTaLufrm2T71fedm6rdao9hMv0SDtEiswXWrn0IL/IB157D0664E2awJn5vzb/ZE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=tFx2oMBl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="tFx2oMBl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B667C4CED1; Wed, 19 Feb 2025 08:56:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1739955384; bh=z4canbL1ccqsuvByLkRhTKXn0wz7D9F/HLO7C0DutrY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tFx2oMBljmNpKeF9wUI7C8yLqO3oDrMfstr7Q5Zd9zdHOS17FVwabqdk4354DKX7I Gk7aHrDRmKUs0+yBQRyF8Hdhw7SBzrnYtMJGh1c6oxMZcXxdVri9zhOJglx1EClxaq iaw6zB5HqCJkLYAk1vn8ivuytv11tRMfRGOg5Pkw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Juri Lelli , "Peter Zijlstra (Intel)" , Phil Auld , Waiman Long Subject: [PATCH 6.12 219/230] sched/deadline: Check bandwidth overflow earlier for hotplug Date: Wed, 19 Feb 2025 09:28:56 +0100 Message-ID: <20250219082610.258219409@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250219082601.683263930@linuxfoundation.org> References: <20250219082601.683263930@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Juri Lelli commit 53916d5fd3c0b658de3463439dd2b7ce765072cb upstream. Currently we check for bandwidth overflow potentially due to hotplug operations at the end of sched_cpu_deactivate(), after the cpu going offline has already been removed from scheduling, active_mask, etc. This can create issues for DEADLINE tasks, as there is a substantial race window between the start of sched_cpu_deactivate() and the moment we possibly decide to roll-back the operation if dl_bw_deactivate() returns failure in cpuset_cpu_inactive(). An example is a throttled task that sees its replenishment timer firing while the cpu it was previously running on is considered offline, but before dl_bw_deactivate() had a chance to say no and roll-back happened. Fix this by directly calling dl_bw_deactivate() first thing in sched_cpu_deactivate() and do the required calculation in the former function considering the cpu passed as an argument as offline already. By doing so we also simplify sched_cpu_deactivate(), as there is no need anymore for any kind of roll-back if we fail early. Signed-off-by: Juri Lelli Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Phil Auld Tested-by: Waiman Long Link: https://lore.kernel.org/r/Zzc1DfPhbvqDDIJR@jlelli-thinkpadt14gen4.remote.csb Signed-off-by: Greg Kroah-Hartman --- kernel/sched/core.c | 22 +++++++--------------- kernel/sched/deadline.c | 12 ++++++++++-- 2 files changed, 17 insertions(+), 17 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8091,19 +8091,14 @@ static void cpuset_cpu_active(void) cpuset_update_active_cpus(); } -static int cpuset_cpu_inactive(unsigned int cpu) +static void cpuset_cpu_inactive(unsigned int cpu) { if (!cpuhp_tasks_frozen) { - int ret = dl_bw_deactivate(cpu); - - if (ret) - return ret; cpuset_update_active_cpus(); } else { num_cpus_frozen++; partition_sched_domains(1, NULL, NULL); } - return 0; } static inline void sched_smt_present_inc(int cpu) @@ -8165,6 +8160,11 @@ int sched_cpu_deactivate(unsigned int cp struct rq *rq = cpu_rq(cpu); int ret; + ret = dl_bw_deactivate(cpu); + + if (ret) + return ret; + /* * Remove CPU from nohz.idle_cpus_mask to prevent participating in * load balancing when not active @@ -8210,15 +8210,7 @@ int sched_cpu_deactivate(unsigned int cp return 0; sched_update_numa(cpu, false); - ret = cpuset_cpu_inactive(cpu); - if (ret) { - sched_smt_present_inc(cpu); - sched_set_rq_online(rq, cpu); - balance_push_set(cpu, false); - set_cpu_active(cpu, true); - sched_update_numa(cpu, true); - return ret; - } + cpuset_cpu_inactive(cpu); sched_domains_numa_masks_clear(cpu); return 0; } --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -3511,6 +3511,13 @@ static int dl_bw_manage(enum dl_bw_reque break; case dl_bw_req_deactivate: /* + * cpu is not off yet, but we need to do the math by + * considering it off already (i.e., what would happen if we + * turn cpu off?). + */ + cap -= arch_scale_cpu_capacity(cpu); + + /* * cpu is going offline and NORMAL tasks will be moved away * from it. We can thus discount dl_server bandwidth * contribution as it won't need to be servicing tasks after @@ -3527,9 +3534,10 @@ static int dl_bw_manage(enum dl_bw_reque if (dl_b->total_bw - fair_server_bw > 0) { /* * Leaving at least one CPU for DEADLINE tasks seems a - * wise thing to do. + * wise thing to do. As said above, cpu is not offline + * yet, so account for that. */ - if (dl_bw_cpus(cpu)) + if (dl_bw_cpus(cpu) - 1) overflow = __dl_overflow(dl_b, cap, fair_server_bw, 0); else overflow = 1;