From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com [63.178.143.178]) (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 354782EBDD6 for ; Thu, 6 Nov 2025 10:54:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=63.178.143.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762426493; cv=none; b=F2GNPpdsiXNWxrbRqJ5ILN43Dr2JxI49mnCtBCzjuoI5+vOEeGQ8rUlFchwp9iq9j5remDl3NK0VzVtUpqW/wpZK1z/Ym1EoLvArHIEKIfP6g6DVGzA0afzCyVdfWNyR8JIWWjy7vjVjEKyCuYpBS3QX1yTiIabpGDxlinSEjF0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762426493; c=relaxed/simple; bh=DynFZPxqfJBP2IZ3HWi01dv0vfrDy6veKMaELHGbcxo=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=G4KCc8UsovD0S4voZQ/QmUiAWufz6OWsQQXR+/u5MX96sFT2ljykBaVzu7zHvbOo5hQA1zOUig3yiu+EIm0rNaVFy6PcPek86eLjsgQe6e6+z6w+vPBOlrlK5GYx4gJqigRviDoQ4z7igf+3ilyBR+zp7B6TXzBUsh9Ti8fCDPI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.com; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b=er/Yl/UY; arc=none smtp.client-ip=63.178.143.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b="er/Yl/UY" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1762426491; x=1793962491; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=DynFZPxqfJBP2IZ3HWi01dv0vfrDy6veKMaELHGbcxo=; b=er/Yl/UYH2srcMJG88pdmOmiOK9pIM9heEwoWlfrgGoOZlJmeWQwuKou G0B335RvUA9sdU55hKsmN8MNdOe+Pi5w2t+sMPZZv0t/hfriLwcKUV/d8 BFph8EFvNir1P6hEgn2NV+vney4874mwRKg+AhJgZT2eWpAW8yk1sEK2g 6ouw81dWJXqQ+W5aBhLiODqoxiixsPk3zmgPaSHb9SES37CrFNQu6pzZ9 mJj/82OcamwpeFjO4e2pmQVTSdchs1D5WO8nirnf+ZjVMinnJpmKnKLRb CBejsO0JNnZD+8QHJAR7GGT31Nb9zkYMCAkpQkPhUPSSZBasqpC1rr0l/ A==; X-CSE-ConnectionGUID: bHgmCL0TSBSormwYKdcUdQ== X-CSE-MsgGUID: Hclk1eRgSWmLfl47kGSP+Q== X-IronPort-AV: E=Sophos;i="6.19,284,1754956800"; d="scan'208";a="4657986" Received: from ip-10-6-11-83.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.11.83]) by internal-fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Nov 2025 10:54:33 +0000 Received: from EX19MTAEUC001.ant.amazon.com [54.240.197.225:19413] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.26.203:2525] with esmtp (Farcaster) id 3077895c-4cab-4a10-babc-fd4d7185d354; Thu, 6 Nov 2025 10:54:32 +0000 (UTC) X-Farcaster-Flow-ID: 3077895c-4cab-4a10-babc-fd4d7185d354 Received: from EX19D003EUB001.ant.amazon.com (10.252.51.97) by EX19MTAEUC001.ant.amazon.com (10.252.51.193) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Thu, 6 Nov 2025 10:54:28 +0000 Received: from u5934974a1cdd59.ant.amazon.com (10.146.13.223) by EX19D003EUB001.ant.amazon.com (10.252.51.97) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Thu, 6 Nov 2025 10:54:17 +0000 From: Fernand Sieber To: CC: , , , , , , , , Subject: Re: [tip:sched/core] [sched/fair] 79104becf4: BUG:kernel_NULL_pointer_dereference,address Date: Thu, 6 Nov 2025 12:54:01 +0200 Message-ID: <20251106105401.220218-1-sieberf@amazon.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251105122808.GK988547@noisy.programming.kicks-ass.net> References: <20251105122808.GK988547@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D035UWA003.ant.amazon.com (10.13.139.86) To EX19D003EUB001.ant.amazon.com (10.252.51.97) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hi Peter, > But yeah, if the task holding your resource is doing yield() you're > 'sad'. Basically a sched-fair yield() means: I've no fucking clue what > I'm doing and lets hope we can make progress a little later. > > And it gets worse in the context of PI/proxy, because in that case your > fair task can deadlock the system through sheer incompetence. > > Anyway, consider the PI case, we bump a fair task to FIFO and then > yield() would do the FIFO yield -- with all the possible problems. > > And we want the same for proxy, if the boosting context is FIFO, we want > a FIFO yield. Alright, makes sense. Based on your suggestion I've submitted a patch: lore.kernel.org/lkml/20251106104022.195157-1-sieberf@amazon.com/T/#u This is essentially the same as your suggestion + handling of yield to and scx. Also confirmed no crashes with this patch + v3 of the vruntime forfeit patch https://lore.kernel.org/lkml/20250918150528.292620-1-sieberf@amazon.com/ --Fernand Amazon Development Centre (South Africa) (Proprietary) Limited 29 Gogosoa Street, Observatory, Cape Town, Western Cape, 7925, South Africa Registration Number: 2004 / 034463 / 07