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 BD4DE3EFFC9; Wed, 7 Oct 2026 20:45:13 +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=1791405915; cv=none; b=EogTvanod+xVDjH0bkOduG9WeFsMvUTuY5sMWDRC3VWRrkq9XVedM0Bek7YDG6yPoWzkgwpjafsDBw43tEEgmrS6Lq7GsXZAHj6j6b+NH0ge86Cplk2H+E58baQPX1JkueJthSIXdIoHitnSjONJ/Zamz7nnqfHCsXsW6jzPm4Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791405915; c=relaxed/simple; bh=BYZMJyO/+mj3bePILNqEL4iPB++fzFXIP/7p8MXrsns=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=QoHBh/Rn/oEo0RLXJAXDxkXdnKTQbqHCKSXW0nM3DY84Y36FHJzU+6FKPmzBHLVf0O1wFKd+5TOBqOwnCr4vgpis3k4KFEpppb+P5brfezfjKEzA7YJQazjzo8eafiIG0YMZJzFSVuxPQ6ga5NbgtTytteNYELnGqsT5F8Tc8nQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eqnJbMxd; 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="eqnJbMxd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 824971F00898; Wed, 7 Oct 2026 20:45:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791405913; bh=JU5z0TM0EOoGd+7UOEnpGgtmwUn17x1HpqFrPRnvV4A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eqnJbMxdZIDSm4SlUyl2i3P3CPQYQBJWn+3SbEAyXVbw6dreC1aSz/PlF6/n5HoAA LHt1/08a2VWa9H/LeuYSbLF4Umsogj1lyp0qSFTV9RX4A0BT7dPg38ENos8MtakNeT ptF6p7zYg/U6DplTuGN1cHhgxYv0N78TjCq934Wn+yZBCF6uZ2b8ZSWpLOKmVohJbN DTCCAjvR9gpgl4r0sMG0fodHDTnjWL+kbUliAqhlgsZBeoyPJBiuc+W/8/q+qLiOyo +cmu/xhTC5ewKkB5jXg4ZVL8PfgKlMQou+0hJ/J5Z7BDL7CWCTGNXLvd7lVRYjmBlU yP+yc5JLkNSfg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 2946ECE1735; Wed, 7 Oct 2026 13:45:13 -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 v2 03/10] rcu: Don't panic on already-ended RCU CPU stalls Date: Wed, 7 Oct 2026 13:45:04 -0700 Message-Id: <20261007204511.1982646-3-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: 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 81d42b6e2e312..01bdbd7e28cca 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 091e7850ab6ec..93ba31a619b67 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