From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 3A842390CB5 for ; Fri, 12 Jun 2026 01:54:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781229244; cv=none; b=D5W/8Mk0xpDI5jdnb4XQKpvKKYYfH4k8ucJyWqVvQu+5HAXIgoCOx42mc0K3F0Oh1huEyclPyUZ++2ZA7S2/+bKoMhiQiN6uoAFIPgIc25UnWu5C74KvhNcxHOZpkQF1mMGJ9zkqzAGelwB7uHlv6zZFTdadmg4oeIIUgYxU8Sc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781229244; c=relaxed/simple; bh=G5htJQtW1I4aqq/VOi01V86P6nJ3uIoz/OkKT4/na7w=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=qgGmER4bhddNA+D7gvnLta2hR0WYmoTcwOd9cc8/rGUTOkFH97nuYd7Q9IW1DlqjyyrzRUlcfP2fakk9OR3OqutdHbhzVVdzpeuv86Ez1iW8mTY3AR+6q2Ugk8zizmazWeWzRf7NQkmBCI86zJfG8SIophqF+bsTeH22bGcNSPc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=surriel.com; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b=TrP1WfQn; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=surriel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b="TrP1WfQn" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=surriel.com ; s=mail; h=MIME-Version:Content-Transfer-Encoding:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=G5htJQtW1I4aqq/VOi01V86P6nJ3uIoz/OkKT4/na7w=; b=TrP1WfQnCEfxo/2TNPqk4NMLbj /wqOeULDvP4osLdPRzOiHzMYuI1rX7fUAMVpoT/UzKxCTtvk2br6ECdwdxc723oozJi+rVoVjdRdT masTFDfZXKgvTGFmLYr4HjUKdMo0D6EUrnwMti70yasJVoGOcVNNv2MBFQ4vLacl2qbX/mzelxPLY QiXup2PHnrqHduj+w9M1Eh+ZUj15qMKoTt3UR7mYA6xGGWNRSNyBi0SUO/6637qCDdjWmm/Pde8xI CJYsSzxJ1mEl3YgE6IT76f3TmZ3xXBX1Flb3UDXIKOTYW0UlleA0l9D+Z7EnFVBsSOCHXIzhTP7wP 8V823KkA==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1wXr5d-000000001FI-2nCT; Thu, 11 Jun 2026 21:53:45 -0400 Message-ID: <91b346ee1dfe88390acb462c9c1a8cb8dc3c2b05.camel@surriel.com> Subject: Re: [PATCH 0/9] sched: make WARN_ON under rq->lock deadlock-safe (SCHED_WARN_ON) From: Rik van Riel To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, vschneid@redhat.com Date: Thu, 11 Jun 2026 21:53:45 -0400 In-Reply-To: <20260611191922.GK187714@noisy.programming.kicks-ass.net> References: <20260611021416.910555-1-riel@surriel.com> <20260611074344.GG48970@noisy.programming.kicks-ass.net> <20260611191922.GK187714@noisy.programming.kicks-ass.net> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2026-06-11 at 21:19 +0200, Peter Zijlstra wrote: >=20 > Myself, I almost exclusively run with earlycon serial and force > printk > to be early_printk() (effectively not using printk at all). This > works > perfectly fine and is the most reliable thing ever. I can push out > characters to the UART from any context. >=20 Great for development, not so good for production. When something like an OOM kill happens, the amount of data printed by the kernel can take a long time to get flushed out a serial port. In fact, it can take long enough to cause things like RCU stalls and soft lockups, and break workloads that way. Having the serial console deferred allows those systems to survive. If the system crashes before the messages were sent out the serial port, the dmesg buffer will be in the vmcore, and get extracted by the crash analysis tooling. It sounds like the printk people may be right with making that behavior an option, since different scenarios require different behavior. --=20 All Rights Reversed.