From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94119C433FE for ; Wed, 15 Dec 2021 16:59:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 189536B0071; Wed, 15 Dec 2021 11:59:06 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 13A496B0073; Wed, 15 Dec 2021 11:59:06 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 001FB6B0074; Wed, 15 Dec 2021 11:59:05 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0188.hostedemail.com [216.40.44.188]) by kanga.kvack.org (Postfix) with ESMTP id E837E6B0071 for ; Wed, 15 Dec 2021 11:59:05 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B32B318024CC6 for ; Wed, 15 Dec 2021 16:58:55 +0000 (UTC) X-FDA: 78920638230.08.4E5B885 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf29.hostedemail.com (Postfix) with ESMTP id 50E60120011 for ; Wed, 15 Dec 2021 16:58:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639587534; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=muCmOAWvr5CQnLclHX0MhSQxoOgFUPCsAa/pyphHI1Y=; b=L4WdolFWgm7EDUZ+CxLoVki4Vi69zUBn9Yc+9X6EeOT7FNu98NSbmn5TozjquSUnUxwQCh +MP7rEhQtQj0aRRQElqDCQm92J+Xj6+AcGHSI8phN8LFM7IAGVn1K2eFdWZx/Flt9jjPLm TOKwoBhGQwbA0PxkoZfIPdNBBi61bC4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-176-XaZxwaWxO3qkA6d1KfTK0w-1; Wed, 15 Dec 2021 11:58:49 -0500 X-MC-Unique: XaZxwaWxO3qkA6d1KfTK0w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C053D2F31; Wed, 15 Dec 2021 16:58:47 +0000 (UTC) Received: from [10.22.10.54] (unknown [10.22.10.54]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6368C57CD2; Wed, 15 Dec 2021 16:58:46 +0000 (UTC) Message-ID: Date: Wed, 15 Dec 2021 11:58:45 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH-next v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT Content-Language: en-US To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Sebastian Andrzej Siewior , Thomas Gleixner References: <20211214144412.447035-1-longman@redhat.com> <20211215043657.ngmxlk6rgc2ysbmz@offworld> From: Waiman Long In-Reply-To: <20211215043657.ngmxlk6rgc2ysbmz@offworld> Content-Type: text/plain; charset=UTF-8; format=flowed X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=L4WdolFW; spf=none (imf29.hostedemail.com: domain of longman@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=longman@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 50E60120011 X-Stat-Signature: oo4ghdksfmq9jdu7wp5c5k3js4u9bz33 X-HE-Tag: 1639587533-304192 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/14/21 23:36, Davidlohr Bueso wrote: > On Tue, 14 Dec 2021, Waiman Long wrote: > >> @@ -2189,7 +2194,7 @@ static void drain_local_stock(struct=20 >> work_struct *dummy) >> =C2=A0=C2=A0=C2=A0=C2=A0 * drain_stock races is that we always operate= on local CPU stock >> =C2=A0=C2=A0=C2=A0=C2=A0 * here with IRQ disabled >> =C2=A0=C2=A0=C2=A0=C2=A0 */ >> -=C2=A0=C2=A0=C2=A0 local_irq_save(flags); >> +=C2=A0=C2=A0=C2=A0 local_lock_irqsave(&memcg_stock.lock, flags); >> >> =C2=A0=C2=A0=C2=A0=C2=A0stock =3D this_cpu_ptr(&memcg_stock); >> =C2=A0=C2=A0=C2=A0=C2=A0drain_obj_stock(&stock->irq_obj); > > So here there is still the problem that you can end up taking sleeping=20 > locks > with irqs disabled via obj_cgroup_put() >> obj_cgroup_release() - ie: t= he > percpu_ref_switch_lock and css_set_lock. It had occurred to me to promo= te > the former to a raw spinlock, but doubt we can get away with the latter= . Yes, it is tricky to avoid all these. One possibility to to delay=20 obj_cgroup_release() through RCU. However, this is outside the scope of=20 this patch. Cheers, Longman