From patchwork Wed Mar 22 19:44:53 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederic Weisbecker X-Patchwork-Id: 73648 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a5d:604a:0:0:0:0:0 with SMTP id j10csp2534592wrt; Wed, 22 Mar 2023 12:46:14 -0700 (PDT) X-Google-Smtp-Source: AK7set89mpsYcg7tZ2mLQe4NLB+zQ5QInI1oZufkG79kZ9Aiux4CTsAW1t++sPBizLYidb/bDePv X-Received: by 2002:a05:6a20:1221:b0:d9:b59c:d09e with SMTP id v33-20020a056a20122100b000d9b59cd09emr655303pzf.11.1679514374162; Wed, 22 Mar 2023 12:46:14 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1679514374; cv=none; d=google.com; s=arc-20160816; b=ZAxdAm+tsuf4UJsU+z1vMKQ3HAfUgLwtobzmoWZgH4JlIHPudAvvNXzC8bWuIh0ny+ xG3jji1uVdX7ljYY3ZCmMkEhhQtnM1V980QlaTwkCraMB4xmi6gwi5CriQARbhvV+mNp rOUgZ27AabsBWSzUejHhCtPEa7FtU2AU0Mh5Pm8/7ogM1BR0dUp8hoOAii1ROcAr1krV TURO+RSvhMVoZgC2jgPyGJ/iy26pZZvLbyqS9KoWsTqWruIEl8yfJrMEbTNWvWY4dU0J SVh2Z7jy7ll0SuKIIL5VJ7FBBS+UBtB9U3FtvLmGkUqQtvrUAkcomw+Qs/5xJ3SaDLlG suSw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=mmglLE5oH+V8Tbw5lSX8yjxfe/MV+7OxcRsttZXtJoU=; b=Bw0WsaC/bynEKeCo0kMuZOZ+ajHCIfHJ+/ZqRjd6vOt4eaPSZbyUX0GOQ4XNu6wLEF 6LvkkpULN5YKY9C/KyK8WcXG8rw64ZT4UZMT58XLJgZ2cBGwyJWtMj5TVkO48SGwB2rk qGa/aivX1eURTKsvwgIF3uO+ItH6YmofMvO1jzIVBDMSEDlBHnbaLUOStatXfvm9saeC Fbvo14XF9z3epum5PtcM9VIdecMuNkprsCr1Nf+X4nvD/7fAjUCClRJo8KLsgK6uu0Uw lWHDFyq43Tl38SowB99Z+Jmn9DLPvL3HO+94doQDspL4MHkfjREI2FkBM+BGjOK+YbuH 05+w== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=KsIagmLy; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id 18-20020a630412000000b004fc29da6e55si16269867pge.674.2023.03.22.12.46.01; Wed, 22 Mar 2023 12:46:14 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=KsIagmLy; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230010AbjCVTpW (ORCPT + 99 others); Wed, 22 Mar 2023 15:45:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52616 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229838AbjCVTpS (ORCPT ); Wed, 22 Mar 2023 15:45:18 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6135E3E0BD; Wed, 22 Mar 2023 12:45:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EF741622B2; Wed, 22 Mar 2023 19:45:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E6C7C4339E; Wed, 22 Mar 2023 19:45:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1679514306; bh=a59gUDfTCHexacSrsbU3Hhq+A3tfJIUWFd5dyE5PoH0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KsIagmLyRTqKsfR7uIUg9MjUB6redqBnrKvV76N6o1Vx+jY7uIq9Y/alf5qVC/2ey ohoXznoXXIOPSCCOrKmSUnBTPG7XgSSOYnAU0cwsvTb1jWWtbM7mUf8bn8zfxUqq7d sUKfStasnjoGheU7ibY1W95SuRdThbFK9Ec/iAOHru2Z9iREVbwiQjm2+mgwBrHgpT Rv8lUWHtGFZv1KFuOaULMtS5KzIMTqZzlDzOsR6T4Fl82KuJ/xakJuFUd6056Ubqmc H7gSghF0E0NFS/fX2z1J5oKfP42YjQUcRkcAmriowRcVz/Mqs+RrElKEEgy3Ag1wLo 1ff65pFu9K4+A== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , rcu , Uladzislau Rezki , Neeraj Upadhyay , Boqun Feng , Joel Fernandes Subject: [PATCH 1/4] rcu/nocb: Protect lazy shrinker against concurrent (de-)offloading Date: Wed, 22 Mar 2023 20:44:53 +0100 Message-Id: <20230322194456.2331527-2-frederic@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230322194456.2331527-1-frederic@kernel.org> References: <20230322194456.2331527-1-frederic@kernel.org> MIME-Version: 1.0 X-Spam-Status: No, score=-5.2 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1761098464543116465?= X-GMAIL-MSGID: =?utf-8?q?1761098464543116465?= The shrinker may run concurrently with callbacks (de-)offloading. As such, calling rcu_nocb_lock() is very dangerous because it does a conditional locking. The worst outcome is that rcu_nocb_lock() doesn't lock but rcu_nocb_unlock() eventually unlocks, or the reverse, creating an imbalance. Fix this with protecting against (de-)offloading using the barrier mutex. Signed-off-by: Frederic Weisbecker --- kernel/rcu/tree_nocb.h | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index f2280616f9d5..dd9b655ae533 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1336,13 +1336,25 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) unsigned long flags; unsigned long count = 0; + /* + * Protect against concurrent (de-)offloading. Otherwise nocb locking + * may be ignored or imbalanced. + */ + mutex_lock(&rcu_state.barrier_mutex); + /* Snapshot count of all CPUs */ for_each_possible_cpu(cpu) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - int _count = READ_ONCE(rdp->lazy_len); + int _count; + + if (!rcu_rdp_is_offloaded(rdp)) + continue; + + _count = READ_ONCE(rdp->lazy_len); if (_count == 0) continue; + rcu_nocb_lock_irqsave(rdp, flags); WRITE_ONCE(rdp->lazy_len, 0); rcu_nocb_unlock_irqrestore(rdp, flags); @@ -1352,6 +1364,9 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) if (sc->nr_to_scan <= 0) break; } + + mutex_unlock(&rcu_state.barrier_mutex); + return count ? count : SHRINK_STOP; }