From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grygorii Strashko Subject: Re: [PATCH v2] reboot: Backup orderly_poweroff Date: Fri, 15 Jan 2016 15:29:04 +0200 Message-ID: <5698F420.2010500@ti.com> References: <1452688405-15087-1-git-send-email-j-keerthy@ti.com> <20160114090520.GA4351@gmail.com> <569767EC.2010704@ti.com> <20160114100913.GB15857@gmail.com> <56977BA7.702@ti.com> <20160114112354.GA17869@gmail.com> <20160114132527.575e0f20@lxorguk.ukuu.org.uk> <20160115101459.GB23349@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160115101459.GB23349@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Ingo Molnar , One Thousand Gnomes Cc: Keerthy , Keerthy , linux-kernel@vger.kernel.org, edubezval@gmail.com, nm@ti.com, linux-pm@vger.kernel.org, linux-omap@vger.kernel.org, joel@jms.id.au, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, peterz@infradead.org, dyoung@redhat.com, josh@joshtriplett.org, mpe@ellerman.id.au, Thomas Gleixner , Peter Zijlstra List-Id: linux-pm@vger.kernel.org On 01/15/2016 12:14 PM, Ingo Molnar wrote: > > * One Thousand Gnomes wrote: > >>> If kernel_power_off() is called then the system should power off. No ifs and >>> whens. >> >> Even if it doesn't the watchdog should kill it. >> >> That is broken on some platforms on the watchdog side as the >> watchdog shuts down during our power off callbacks - because the system >> firmware is too stupid to reset the watchdog as it powers back up (so >> keeps rebooting). >> >> If you watchdog and firmware function properly you shouldn't even have to >> care if you crash during the kernel power off. > > That's a good point as well - if the system is 'stuck' for some notion of stuck, > then watchdog drivers can help. > Seems ARM doesn't have endless loop implemented in machine_power_off() - so, not too much chances for Watchdog to fire. void machine_power_off(void) { local_irq_disable(); smp_send_stop(); if (pm_power_off) pm_power_off(); --- endless loop ? --- or restart ? } [and even if it will be there - 20-30sec is usual timeout for Watchdog and this enough time to burn the system in case of thermal emergency poweroff :(] > Here it's unclear whether user-space even called the sys_reboot() system call. > That's true - original log [1] has Nov 30 11:19:22 [ 5.942769] thermal thermal_zone3: critical temperature reached(108 C),shutting down [...] Nov 30 11:19:24 [ 7.387900] ahci 4a140000.sata: flags: 64bit ncq sntf stag pm led clo only pmp pio slum part ccc apst Nov 30 11:19:24 INIT: Switching to runlevel: 0 Nov 30 11:19:24 INIT: Sending processes the TERM signal and there are no [ 220.004522] reboot: Power down Also, It's not the first time this part of code is discussed (thermal emergency poweroff) [2], so the good question, as for me, is it really required and safe to use orderly_poweroff() in case of thermal emergency poweroff ([3] as example)? In general, this kind of use case can be simulated using SysRq on any arch - [3.290034] Freeing unused kernel memory: 492K (c0a67000 - c0ae2000) INIT: version 2.88 booting Starting udev ^^ The issue most probably might happens when system in the process of loading modules So, once modules loading process is started - fire Sysrq "poweroff(o)" [1] http://pastebin.ubuntu.com/14326688/ [2] https://lkml.org/lkml/2012/9/18/577 [3] http://review.omapzoom.org/#/c/34898/ -- regards, -grygorii