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 320672E645 for ; Mon, 14 Apr 2025 19:59:21 +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=1744660776; cv=none; b=a7DdLx8iWEiZWCvr/iVpdR75gSNvIxoeW4sEgB72rs7FCgrjKnXuBhmrWMVbDVAWQP3tRN/3qiaaXk5s1Aay8OHWXIVVDv5WP8cJM2myrtbk+HwpIpJNPxBMeh0hobUO9kGEOeqUIuzhG1Smf64RpTTfaaVHczmtQeHK6oD+oGI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744660776; c=relaxed/simple; bh=fsg/taSW2kmNNFQ5qf+vjE9sbZlgyP3G1l/VQPoGKms=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=ZhaSwya1TRHvuz1nTDojvrtcybejb6Ut0u6fpAO4CPfDOvNHyxjSH+sTRhQ3OU1aAgnp6rrCLTjKjQX2tS9Y5d10HISfTeNoXeMaKzSx2rctBDbDr2jQsXzMrR3yZFeA7BaW1Lf0y1iKbcznN+cHC+9tltz1erakqVB1GKITJSs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=shelob.surriel.com; 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=shelob.surriel.com 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 1u4Pw6-000000003uv-1e2J; Mon, 14 Apr 2025 15:57:42 -0400 Message-ID: Subject: Re: [PATCH] sched/fair: Add null pointer check to pick_next_entity() From: Rik van Riel To: Peter Zijlstra Cc: Chris Mason , Pat Cody , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, patcody@meta.com, kernel-team@meta.com, Breno Leitao Date: Mon, 14 Apr 2025 15:57:42 -0400 In-Reply-To: <20250402082221.GT5880@noisy.programming.kicks-ass.net> References: <20250320205310.779888-1-pat@patcody.io> <20250324115613.GD14944@noisy.programming.kicks-ass.net> <7B2CFC16-1ADE-4565-B555-7525A50494C2@surriel.com> <20250402082221.GT5880@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 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: riel@surriel.com On Wed, 2025-04-02 at 10:22 +0200, Peter Zijlstra wrote: >=20 > Please confirm what the reason for overflow is. >=20 Running a large enough sample size has its benefits. We have hit 3 out of the 4 warnings below. The only one we did not hit is the cfs_rq->avg_load !=3D avg_load warning. Most of the time we seem to hit the warnings from the code that removes tasks from the runqueue, but we are occasionally seeing it when adding tasks to the runqueue, as well. > +++ b/kernel/sched/fair.c > @@ -620,12 +620,36 @@ static inline s64 entity_key(struct cfs_ > =C2=A0 * > =C2=A0 * As measured, the max (key * weight) value was ~44 bits for a > kernel build. > =C2=A0 */ > + > +static void avg_vruntime_validate(struct cfs_rq *cfs_rq) > +{ > + unsigned long load =3D 0; > + s64 vruntime =3D 0; > + > + for (struct rb_node *node =3D rb_first_cached(&cfs_rq- > >tasks_timeline); > + =C2=A0=C2=A0=C2=A0=C2=A0 node; node =3D rb_next(node)) { > + struct sched_entity *se =3D __node_2_se(node); > + unsigned long weight =3D scale_load_down(se- > >load.weight); > + s64 key =3D entity_key(cfs_rq, se); > + /* vruntime +=3D key * weight; */ > + WARN_ON_ONCE(__builtin_mul_overflow(key, weight, > &key)); > + WARN_ON_ONCE(__builtin_add_overflow(vruntime, key, > &vruntime)); > + load +=3D weight; > + } > + > + WARN_ON_ONCE(cfs_rq->avg_load !=3D load); > + WARN_ON_ONCE(cfs_rq->avg_vruntime !=3D vruntime); > +} > + > =C2=A0static void > =C2=A0avg_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se) > =C2=A0{ > =C2=A0 unsigned long weight =3D scale_load_down(se->load.weight); > =C2=A0 s64 key =3D entity_key(cfs_rq, se); > =C2=A0 > + /* not yet added to tree */ > + avg_vruntime_validate(cfs_rq); > + > =C2=A0 cfs_rq->avg_vruntime +=3D key * weight; > =C2=A0 cfs_rq->avg_load +=3D weight; > =C2=A0} > @@ -638,6 +662,9 @@ avg_vruntime_sub(struct cfs_rq *cfs_rq, > =C2=A0 > =C2=A0 cfs_rq->avg_vruntime -=3D key * weight; > =C2=A0 cfs_rq->avg_load -=3D weight; > + > + /* already removed from tree */ > + avg_vruntime_validate(cfs_rq); > =C2=A0} > =C2=A0 > =C2=A0static inline >=20 --=20 All Rights Reversed.