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: 13184540 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C11EC76196 for ; Wed, 22 Mar 2023 19:45:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229836AbjCVTpT (ORCPT ); Wed, 22 Mar 2023 15:45:19 -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 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org 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; }