From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 EBFA82EB84E; Sat, 19 Sep 2026 00:29:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789777743; cv=none; b=uulbjMmI1EdVAW0K32I9HAXxmdtsJqB8ZlRnw78rsB2g74V392lhJj6Uj5ShvchUlLO3VgPnSki+/fY3gvQ4KeXtZn8wQgdFZYfuLx9wuDBa7nTUfeQXj6HUBBg5k5gt5w5LpprzBNoS7N3HOXVBHjsi9y94el7YK2XmE5gIT7U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789777743; c=relaxed/simple; bh=jRSA949A5wspjX5p87+QLwsJGx3QqRlWQ+q7KtAGYE0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=J9aKnyrSJ23KEBQOdtdO1JyRu2606nEwzmiQW57AmSl/dpyTKVaj1MTFekrEcXUSFih+KJbpompbvA9DFir1HYoEqGnO8VASbyQYM41GEejjBCqYs9j7G/mtPD4dd9hSlZB+bY/gwnPj2rDMvYKL4zLQ527gxSRTaAsRY1tLJ0Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eAIPCaeA; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eAIPCaeA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E7AB1F00899; Sat, 19 Sep 2026 00:29:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789777741; bh=NfRsui4HeEGNdMbX4Kuk3a2ehlsQZZj6609HvU+UOBc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eAIPCaeAlaU+WiFOa/N9bLENaAvute8QCYcs16pOdjZU3IdNWqa+VKbV03f3ebRlN 9rrVZI3d07NIZIuSydAMWan2vXUJdMiMPHdUP57gFRTaqpSrfDAH6QqNKCqJq9peF0 ysWb3eiGnHRq0GF21Zm+GCrmWSl1bTRbFTLsF05dZIMfvmLBZxMY7/VW7d+ARgBN2J ebb2yIrqTw3f3sZCp/hWiw86M1kE054/VtlDVGc9qhabgMQRwuFRTVJtbJg+xSMP5C hxpdDvAfusq6RBXCrRxZqJFzCCHbrwhjFq0A5KCdNoiyG1VCxFfG/AS1B9yD4jmLP3 H9mnuwgxSWdfA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 4D1EBCE17BD; Fri, 18 Sep 2026 17:29:01 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH 3/9] rcu: Don't panic on already-ended RCU CPU stalls Date: Fri, 18 Sep 2026 17:28:54 -0700 Message-Id: <20260919002900.3134117-3-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <7dc2d858-44cc-4efa-8e94-1fe27d691f2b@paulmck-laptop> References: <7dc2d858-44cc-4efa-8e94-1fe27d691f2b@paulmck-laptop> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The current RCU CPU stall-warning code can say "INFO: Stall ended before state dump start" but then panic the system anyway. This commit therefore avoids panicking the system if the stall has already ended. However, the sched_ext scheduler will still be ejected, as it might have been the cause of the almost stall. This can easily be changed if needed. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_exp.h | 2 +- kernel/rcu/tree_stall.h | 12 +++++++++--- 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 81d42b6e2e31..01bdbd7e28cc 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -678,7 +678,7 @@ static void synchronize_rcu_expedited_wait(void) nbcon_cpu_emergency_exit(); - panic_on_rcu_stall(&rcu_exp_stall_cpumask); + panic_on_rcu_stall(&rcu_exp_stall_cpumask, NULL, 0); } } diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 091e7850ab6e..93ba31a619b6 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -159,7 +159,8 @@ static int __init check_cpu_stall_init(void) early_initcall(check_cpu_stall_init); /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */ -static void panic_on_rcu_stall(const struct cpumask *stalled_mask) +static void panic_on_rcu_stall(const struct cpumask *stalled_mask, + unsigned long *gsp, unsigned long gp_seq) { static int cpu_stall; @@ -170,6 +171,11 @@ static void panic_on_rcu_stall(const struct cpumask *stalled_mask) if (scx_rcu_cpu_stall(stalled_mask)) return; + if (gsp && rcu_seq_current(gsp) != gp_seq) { + pr_err("INFO: Stall ended before panic check.\n"); + return; + } + if (++cpu_stall < sysctl_max_rcu_stall_to_panic) return; @@ -703,7 +709,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) nbcon_cpu_emergency_exit(); - panic_on_rcu_stall(&rcu_stall_cpumask); + panic_on_rcu_stall(&rcu_stall_cpumask, &rcu_state.gp_seq, gp_seq); rcu_force_quiescent_state(); /* Kick them all. */ } @@ -758,7 +764,7 @@ static void print_cpu_stall(unsigned long gp_seq, unsigned long gps) cpumask_clear(&rcu_stall_cpumask); cpumask_set_cpu(smp_processor_id(), &rcu_stall_cpumask); - panic_on_rcu_stall(&rcu_stall_cpumask); + panic_on_rcu_stall(&rcu_stall_cpumask, &rcu_state.gp_seq, gp_seq); /* * Attempt to revive the RCU machinery by forcing a context switch. -- 2.40.1