From patchwork Wed Mar 29 16:02:00 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederic Weisbecker X-Patchwork-Id: 76700 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:b0ea:0:b0:3b6:4342:cba0 with SMTP id b10csp534696vqo; Wed, 29 Mar 2023 09:22:52 -0700 (PDT) X-Google-Smtp-Source: AKy350Z+mxAiWECuKhjAaxfiuASyIVmUSMXhYVY7oiQtaUhyOX+gcGqOw/PAhMeM6mmYQP0DvOra X-Received: by 2002:a17:907:2063:b0:92e:d6e6:d8a4 with SMTP id qp3-20020a170907206300b0092ed6e6d8a4mr19697916ejb.44.1680106972537; Wed, 29 Mar 2023 09:22:52 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1680106972; cv=none; d=google.com; s=arc-20160816; b=cqCWF5btYlt9859kMXav29enerh1lyZy+9T7vBEcUVtTrG01TG/bk4m/Q912hTA/3O MkLATkJhkZX/ufo6/paqyDBd8CSFbvdQsMGrNFmUY88mKVcGFkdkwdj4RdBnx9Kcz2qy EZOM9fMy+WriH/zm8dIRR4XnNHw2y3IgxAo241D6V7y09Jc2jWXNWNXVtaJ4yWoEYRF7 LH8JY87cXplTskonv2dQlnsMCCfvWJ83h44JX7K88M3+VLaqNeFjVDXmWJjj+moGRRVg 7Q87L4M37o3rcElJ1pi9OgTS3hyMxhCjN3TC6EcVlCb+nYZsAZu4D5JFqC9fbVqIyJl9 QRvw== 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=1FdTF/dkJtJfmYs6OZ2NwpuUcaQOn4VutCH6oNYKohw=; b=N4MMG6v4Jclk5dIcBTHiAh5irLrhhqWUmBi5yfdTvYnqQRQ0CcGLEf8GG3fI03j2ri ARLoAKMztfwSsh42+Z8CiCV/ps/R0icKwvG/MgoR47fUEf0yWYkOtorPr4HoFY8jD6O9 bn/zprGtQY/FHjWvn4wBH5wATjgeN7YopomZZWRs/89wXiDIK7zGotyLCvdIGJi+UTXh e9jU1v/ajHO5C5DEJ6LfZFmc5q9KZEZ6cEuTwwnBzb0DT4EjiFYTf7n1g7fa9nBQyJva 8Xlzki2aNk16vJuEQhC9mcgauvPA3CIOgUZcCN7ye36+6RlBN5sjsxrcws57i9IdsBzx taTg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=GXJMVZfZ; 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 j24-20020a170906255800b008d7f2747fd8si29568426ejb.161.2023.03.29.09.22.28; Wed, 29 Mar 2023 09:22:52 -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=GXJMVZfZ; 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 S231150AbjC2QFI (ORCPT + 99 others); Wed, 29 Mar 2023 12:05:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60162 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231178AbjC2QEf (ORCPT ); Wed, 29 Mar 2023 12:04:35 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 157F47DBA; Wed, 29 Mar 2023 09:03:31 -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 CA5CA61DA0; Wed, 29 Mar 2023 16:02:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 76468C433EF; Wed, 29 Mar 2023 16:02:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1680105731; bh=Fp/ndTMmWDQvJYRUYSiB/n1pWGiQmprjbLIvXN1t7Yo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GXJMVZfZjTUnt6ouzt7l7m2vLdEpVbUYF3zXJObcVdJJ25rx/QAGDa+UpVUX5FE0p yr9Nrt6tM4pt81wfx84r5lPmsnUfyLbv3QrLoXbP+LziiVJ06zK3GQsjq+RFuVFwiq v/5qNkDMeWEGa054oW0J6Lk4jzXytIB0ApwtctH1DbKmdcqmNH0qiX5j553slYPOp5 aaTi7iyeF5s8UlNX+OkcbFgJMznNcCAKMSsCCYFsqremZD8TJRiiv6HxfgLeXT3yDy 7Z//tvu6PB1lD4HVnV8kem77vQWp8PlIRW8pyBKiBT1n6SzZs5RnfTlJ2C+xWJMZaU 7Qo2OdpvBGN6g== 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, 29 Mar 2023 18:02:00 +0200 Message-Id: <20230329160203.191380-2-frederic@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230329160203.191380-1-frederic@kernel.org> References: <20230329160203.191380-1-frederic@kernel.org> MIME-Version: 1.0 X-Spam-Status: No, score=-2.5 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,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?1761719848720012779?= X-GMAIL-MSGID: =?utf-8?q?1761719848720012779?= 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. Although if the barrier mutex is contended, which should be rare, then step aside so as not to trigger a mutex VS allocation dependency chain. Signed-off-by: Frederic Weisbecker --- kernel/rcu/tree_nocb.h | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index f2280616f9d5..1a86883902ce 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1336,13 +1336,33 @@ 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. + */ + if (!mutex_trylock(&rcu_state.barrier_mutex)) { + /* + * But really don't insist if barrier_mutex is contended since we + * can't guarantee that it will never engage in a dependency + * chain involving memory allocation. The lock is seldom contended + * anyway. + */ + return 0; + } + /* 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 +1372,9 @@ 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; }