From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 96E6F1170E for ; Mon, 11 Sep 2023 14:19:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 18175C433C7; Mon, 11 Sep 2023 14:18:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1694441940; bh=mghLdZhVXHiWOKJrjjWPBLyVbnl5BjhVdqA438YxjsE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=msiYY/JbIVxFWw+rwG6tnB2NS1+esCCB797ZeQbqX9x2tu6Bb77Mc+YDT5Fvedn+J J4ToooboeUjIWyVCUTF+p+6hs8JKsi14Tgb+X8rl4U4Ecug+gxXltGcer/sbU3sk19 BF+osGA/chsLSbfMTr9Hcpu0cyP976MgHmlyVqSU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Paul Gortmaker , Thomas Gleixner , Ahmad Fatoum , Wen Yang , Frederic Weisbecker , Sasha Levin Subject: [PATCH 6.5 590/739] tick/rcu: Fix false positive "softirq work is pending" messages Date: Mon, 11 Sep 2023 15:46:29 +0200 Message-ID: <20230911134707.581318743@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230911134650.921299741@linuxfoundation.org> References: <20230911134650.921299741@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul Gortmaker [ Upstream commit 96c1fa04f089a7e977a44e4e8fdc92e81be20bef ] In commit 0345691b24c0 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the new function report_idle_softirq() was created by breaking code out of the existing can_stop_idle_tick() for kernels v5.18 and newer. In doing so, the code essentially went from a one conditional: if (a && b && c) warn(); to a three conditional: if (!a) return; if (!b) return; if (!c) return; warn(); But that conversion got the condition for the RT specific local_bh_blocked() wrong. The original condition was: !local_bh_blocked() but the conversion failed to negate it so it ended up as: if (!local_bh_blocked()) return false; This issue lay dormant until another fixup for the same commit was added in commit a7e282c77785 ("tick/rcu: Fix bogus ratelimit condition"). This commit realized the ratelimit was essentially set to zero instead of ten, and hence *no* softirq pending messages would ever be issued. Once this commit was backported via linux-stable, both the v6.1 and v6.4 preempt-rt kernels started printing out 10 instances of this at boot: NOHZ tick-stop error: local softirq work is pending, handler #80!!! Remove the negation and return when local_bh_blocked() evaluates to true to bring the correct behaviour back. Fixes: 0345691b24c0 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") Signed-off-by: Paul Gortmaker Signed-off-by: Thomas Gleixner Tested-by: Ahmad Fatoum Reviewed-by: Wen Yang Acked-by: Frederic Weisbecker Link: https://lore.kernel.org/r/20230818200757.1808398-1-paul.gortmaker@windriver.com Signed-off-by: Sasha Levin --- kernel/time/tick-sched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 4df14db4da490..87015e9deacc9 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -1045,7 +1045,7 @@ static bool report_idle_softirq(void) return false; /* On RT, softirqs handling may be waiting on some lock */ - if (!local_bh_blocked()) + if (local_bh_blocked()) return false; pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n", -- 2.40.1