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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:36372) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1iSe1V-0002Wx-GV; Thu, 07 Nov 2019 09:24:13 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1iSe1M-0004tP-DR; Thu, 07 Nov 2019 09:24:04 +0000 Date: Thu, 7 Nov 2019 09:24:04 +0000 From: Russell King - ARM Linux admin To: Lvqiang Subject: Re: [PATCH] ARM: check __ex_table in do_bad() Message-ID: <20191107092404.GV25745@shell.armlinux.org.uk> References: <1573112713-10115-1-git-send-email-Lvqiang.Huang@unisoc.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1573112713-10115-1-git-send-email-Lvqiang.Huang@unisoc.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191107_012456_683294_F14436C0 X-CRM114-Status: GOOD ( 11.01 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: f.fainelli@gmail.com, anshuman.khandual@arm.com, dave.hansen@linux.intel.com, linux-kernel@vger.kernel.org, ebiederm@xmission.com, akpm@linux-foundation.org, will@kernel.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Nov 07, 2019 at 03:45:13PM +0800, Lvqiang wrote: > > We got many crashs in for_each_frame+0x18 arch/arm/lib/backtrace.S > 1003: ldr r2, [sv_pc, #-4] > > The backtrace is > dump_backtrace > show_stack > sched_show_task > show_state_filter > sysrq_handle_showstate_blocked > __handle_sysrq > write_sysrq_trigger > proc_reg_write > __vfs_write > vfs_write > sys_write > > Related Kernel config > CONFIG_CPU_SW_DOMAIN_PAN=y > # CONFIG_ARM_UNWIND is not set > CONFIG_FRAME_POINTER=y > > The task A was dumping the stack of an UN task B. However, the task B What is "an UN task B"? > scheduled to run on another CPU, which cause it stack content changed. > Then, task A may hit a page domain fault and die(). > [520.661314] Unhandled fault: page domain fault (0x01b) at 0x32848c02 So, the backtrace code is trying to access userspace. It isn't supposed to be accessing userspace - there are no guarantees that userspace will be using frame pointers. That is the bug. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel