From patchwork Mon Mar 1 16:10:36 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 390091 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F6C4C433DB for ; Mon, 1 Mar 2021 17:02:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 190E465114 for ; Mon, 1 Mar 2021 17:02:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236617AbhCARCU (ORCPT ); Mon, 1 Mar 2021 12:02:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:54866 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235958AbhCAQzq (ORCPT ); Mon, 1 Mar 2021 11:55:46 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9B0A264FD3; Mon, 1 Mar 2021 16:35:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614616556; bh=FuseDVXj7uPs4R986ds/nEqPJ0f2+6eEryWP/n+yEO0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1+1/DeKAPMkyeIof1mxeC4tK3v6CNx2PLHJOzmXYG+0okWxQCL64jHb9+x45ztARx n3OD97hlSU7QHCZjtSVt4uopKXGBHaEondYCocCgCzeBguLec94kjvp+M+KPsAan4f yzfYaFCFho55Uxl+fwYpc5tE71m1ATyk5rL+F1x8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jakub Kicinski , "Peter Zijlstra (Intel)" , Andrew Morton , Linus Torvalds , "Paul E. McKenney" , Thomas Gleixner , Will Deacon , ard.biesheuvel@linaro.org, oss-drivers@netronome.com, pbonzini@redhat.com, Ingo Molnar , Will McVicker Subject: [PATCH 4.19 016/247] locking/static_key: Fix false positive warnings on concurrent dec/inc Date: Mon, 1 Mar 2021 17:10:36 +0100 Message-Id: <20210301161032.484926340@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161031.684018251@linuxfoundation.org> References: <20210301161031.684018251@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Peter Zijlstra commit a1247d06d01045d7ab2882a9c074fbf21137c690 upstream. Even though the atomic_dec_and_mutex_lock() in __static_key_slow_dec_cpuslocked() can never see a negative value in key->enabled the subsequent sanity check is re-reading key->enabled, which may have been set to -1 in the meantime by static_key_slow_inc_cpuslocked(). CPU A CPU B __static_key_slow_dec_cpuslocked(): static_key_slow_inc_cpuslocked(): # enabled = 1 atomic_dec_and_mutex_lock() # enabled = 0 atomic_read() == 0 atomic_set(-1) # enabled = -1 val = atomic_read() # Oops - val == -1! The test case is TCP's clean_acked_data_enable() / clean_acked_data_disable() as tickled by KTLS (net/ktls). Suggested-by: Jakub Kicinski Reported-by: Jakub Kicinski Tested-by: Jakub Kicinski Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Cc: ard.biesheuvel@linaro.org Cc: oss-drivers@netronome.com Cc: pbonzini@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Will McVicker Signed-off-by: Greg Kroah-Hartman --- kernel/jump_label.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -186,6 +186,8 @@ static void __static_key_slow_dec_cpuslo unsigned long rate_limit, struct delayed_work *work) { + int val; + lockdep_assert_cpus_held(); /* @@ -195,17 +197,20 @@ static void __static_key_slow_dec_cpuslo * returns is unbalanced, because all other static_key_slow_inc() * instances block while the update is in progress. */ - if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) { - WARN(atomic_read(&key->enabled) < 0, - "jump label: negative count!\n"); + val = atomic_fetch_add_unless(&key->enabled, -1, 1); + if (val != 1) { + WARN(val < 0, "jump label: negative count!\n"); return; } - if (rate_limit) { - atomic_inc(&key->enabled); - schedule_delayed_work(work, rate_limit); - } else { - jump_label_update(key); + jump_label_lock(); + if (atomic_dec_and_test(&key->enabled)) { + if (rate_limit) { + atomic_inc(&key->enabled); + schedule_delayed_work(work, rate_limit); + } else { + jump_label_update(key); + } } jump_label_unlock(); }