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 668BC8F5D for ; Thu, 31 Aug 2023 11:11:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDC42C433C7; Thu, 31 Aug 2023 11:11:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1693480268; bh=dVGx34XKhF9qLcX/dUSGr2FW0RwgQThVU0dEsVtfwOg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oChRENr1MZvpmobuR4pKZx/05dQXtJNRFekUmJTPOI3UzhAxQRxZuOHBjA8tpoNX3 tOtwlu8QddPSun/yEFCu373Y1RQCKH1hgsOSQCStSVK5Ggjxibhn/H+TN6/i3aX6ZA 065to+/FaBymuw/U71feIgmvZ6JmNm0bhzo5AiHs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Paul E. McKenney" , "Joel Fernandes (Google)" Subject: [PATCH 5.15 6/9] rcu: Prevent expedited GP from enabling tick on offline CPU Date: Thu, 31 Aug 2023 13:10:14 +0200 Message-ID: <20230831110830.333802009@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230831110830.039135096@linuxfoundation.org> References: <20230831110830.039135096@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul E. McKenney commit 147f04b14adde831eb4a0a1e378667429732f9e8 upstream. If an RCU expedited grace period starts just when a CPU is in the process of going offline, so that the outgoing CPU has completed its pass through stop-machine but has not yet completed its final dive into the idle loop, RCU will attempt to enable that CPU's scheduling-clock tick via a call to tick_dep_set_cpu(). For this to happen, that CPU has to have been online when the expedited grace period completed its CPU-selection phase. This is pointless: The outgoing CPU has interrupts disabled, so it cannot take a scheduling-clock tick anyway. In addition, the tick_dep_set_cpu() function's eventual call to irq_work_queue_on() will splat as follows: smpboot: CPU 1 is now offline WARNING: CPU: 6 PID: 124 at kernel/irq_work.c:95 +irq_work_queue_on+0x57/0x60 Modules linked in: CPU: 6 PID: 124 Comm: kworker/6:2 Not tainted 5.15.0-rc1+ #3 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS +rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014 Workqueue: rcu_gp wait_rcu_exp_gp RIP: 0010:irq_work_queue_on+0x57/0x60 Code: 8b 05 1d c7 ea 62 a9 00 00 f0 00 75 21 4c 89 ce 44 89 c7 e8 +9b 37 fa ff ba 01 00 00 00 89 d0 c3 4c 89 cf e8 3b ff ff ff eb ee <0f> 0b eb b7 +0f 0b eb db 90 48 c7 c0 98 2a 02 00 65 48 03 05 91 6f RSP: 0000:ffffb12cc038fe48 EFLAGS: 00010282 RAX: 0000000000000001 RBX: 0000000000005208 RCX: 0000000000000020 RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffff9ad01f45a680 RBP: 000000000004c990 R08: 0000000000000001 R09: ffff9ad01f45a680 R10: ffffb12cc0317db0 R11: 0000000000000001 R12: 00000000fffecee8 R13: 0000000000000001 R14: 0000000000026980 R15: ffffffff9e53ae00 FS: 0000000000000000(0000) GS:ffff9ad01f580000(0000) +knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000000de0c000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: tick_nohz_dep_set_cpu+0x59/0x70 rcu_exp_wait_wake+0x54e/0x870 ? sync_rcu_exp_select_cpus+0x1fc/0x390 process_one_work+0x1ef/0x3c0 ? process_one_work+0x3c0/0x3c0 worker_thread+0x28/0x3c0 ? process_one_work+0x3c0/0x3c0 kthread+0x115/0x140 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 ---[ end trace c5bf75eb6aa80bc6 ]--- This commit therefore avoids invoking tick_dep_set_cpu() on offlined CPUs to limit both futility and false-positive splats. Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/rcu/tree_exp.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -507,7 +507,10 @@ static void synchronize_rcu_expedited_wa if (rdp->rcu_forced_tick_exp) continue; rdp->rcu_forced_tick_exp = true; - tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); + preempt_disable(); + if (cpu_online(cpu)) + tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); + preempt_enable(); } } j = READ_ONCE(jiffies_till_first_fqs);