From mboxrd@z Thu Jan 1 00:00:00 1970 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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 5A560C433DF for ; Tue, 7 Jul 2020 15:11:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3187D2065D for ; Tue, 7 Jul 2020 15:11:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594134697; bh=o3/8Vod5/obeS6mk6d1i5GHU1cnNiLkoIOiDVUugg8U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=OnJjO11apjSEdUKU2VfK1nDRanvpJhY5bQ2CoXwNP/EwDg2+wTdJuUCF5pugP6pDJ 2hoEsphnK3ZZTLt5fpMEo4QDYvnW5RoWI2M04/qNs27NxDt030BEFsb8i4za2BraC0 J4T+XSM0wJ3SRwBadCGUVmPTfRcTLDEAdiujYoRI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728714AbgGGPLg (ORCPT ); Tue, 7 Jul 2020 11:11:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:52092 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728603AbgGGPLJ (ORCPT ); Tue, 7 Jul 2020 11:11:09 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 389E92065D; Tue, 7 Jul 2020 15:11:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594134668; bh=o3/8Vod5/obeS6mk6d1i5GHU1cnNiLkoIOiDVUugg8U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qppwUxccCfRHi4tPOZ2i/d9l0RaUEu6mUtqEtOn4RdvrkN08Bffg/Jluun02VyXle 8kXe6mqHklysp3ytpvrGQdB2adgivhZoYIGiN4Y7hyztv6SFzc5LOUGUz1L7gtLRVH ku7k+v7Cl2p/JkPmTCezemqebPGBtv7h6bnxGtac= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Douglas Anderson , Daniel Thompson , Sasha Levin Subject: [PATCH 4.4 07/19] kgdb: Avoid suspicious RCU usage warning Date: Tue, 7 Jul 2020 17:10:10 +0200 Message-Id: <20200707145747.873532998@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200707145747.493710555@linuxfoundation.org> References: <20200707145747.493710555@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Douglas Anderson [ Upstream commit 440ab9e10e2e6e5fd677473ee6f9e3af0f6904d6 ] At times when I'm using kgdb I see a splat on my console about suspicious RCU usage. I managed to come up with a case that could reproduce this that looked like this: WARNING: suspicious RCU usage 5.7.0-rc4+ #609 Not tainted ----------------------------- kernel/pid.c:395 find_task_by_pid_ns() needs rcu_read_lock() protection! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 3 locks held by swapper/0/1: #0: ffffff81b6b8e988 (&dev->mutex){....}-{3:3}, at: __device_attach+0x40/0x13c #1: ffffffd01109e9e8 (dbg_master_lock){....}-{2:2}, at: kgdb_cpu_enter+0x20c/0x7ac #2: ffffffd01109ea90 (dbg_slave_lock){....}-{2:2}, at: kgdb_cpu_enter+0x3ec/0x7ac stack backtrace: CPU: 7 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc4+ #609 Hardware name: Google Cheza (rev3+) (DT) Call trace: dump_backtrace+0x0/0x1b8 show_stack+0x1c/0x24 dump_stack+0xd4/0x134 lockdep_rcu_suspicious+0xf0/0x100 find_task_by_pid_ns+0x5c/0x80 getthread+0x8c/0xb0 gdb_serial_stub+0x9d4/0xd04 kgdb_cpu_enter+0x284/0x7ac kgdb_handle_exception+0x174/0x20c kgdb_brk_fn+0x24/0x30 call_break_hook+0x6c/0x7c brk_handler+0x20/0x5c do_debug_exception+0x1c8/0x22c el1_sync_handler+0x3c/0xe4 el1_sync+0x7c/0x100 rpmh_rsc_probe+0x38/0x420 platform_drv_probe+0x94/0xb4 really_probe+0x134/0x300 driver_probe_device+0x68/0x100 __device_attach_driver+0x90/0xa8 bus_for_each_drv+0x84/0xcc __device_attach+0xb4/0x13c device_initial_probe+0x18/0x20 bus_probe_device+0x38/0x98 device_add+0x38c/0x420 If I understand properly we should just be able to blanket kgdb under one big RCU read lock and the problem should go away. We'll add it to the beast-of-a-function known as kgdb_cpu_enter(). With this I no longer get any splats and things seem to work fine. Signed-off-by: Douglas Anderson Link: https://lore.kernel.org/r/20200602154729.v2.1.I70e0d4fd46d5ed2aaf0c98a355e8e1b7a5bb7e4e@changeid Signed-off-by: Daniel Thompson Signed-off-by: Sasha Levin --- kernel/debug/debug_core.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c index 9c939c6bf21cb..321ccdbb73649 100644 --- a/kernel/debug/debug_core.c +++ b/kernel/debug/debug_core.c @@ -488,6 +488,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs, arch_kgdb_ops.disable_hw_break(regs); acquirelock: + rcu_read_lock(); /* * Interrupts will be restored by the 'trap return' code, except when * single stepping. @@ -542,6 +543,7 @@ return_normal: atomic_dec(&slaves_in_kgdb); dbg_touch_watchdogs(); local_irq_restore(flags); + rcu_read_unlock(); return 0; } cpu_relax(); @@ -560,6 +562,7 @@ return_normal: raw_spin_unlock(&dbg_master_lock); dbg_touch_watchdogs(); local_irq_restore(flags); + rcu_read_unlock(); goto acquirelock; } @@ -677,6 +680,7 @@ kgdb_restore: raw_spin_unlock(&dbg_master_lock); dbg_touch_watchdogs(); local_irq_restore(flags); + rcu_read_unlock(); return kgdb_info[cpu].ret_state; } -- 2.25.1