| Message ID | 1346682298-13958-1-git-send-email-shawn.guo@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 3 Sep 2012 22:24:58 +0800 Shawn Guo <shawn.guo@linaro.org> wrote: > Like kernel_power_off calls disable_nonboot_cpus, we may want to have > kernel_restart call disable_nonboot_cpus as well. Doing so can help > the machines that require boot cpu be the last alive cpu during reboot > to survive with kernel restart. That does sound logical. But the changelog is very vague and fluffy. Does this patch actually fix any known problem on any known machine? > ... > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -368,6 +368,7 @@ EXPORT_SYMBOL(unregister_reboot_notifier); > void kernel_restart(char *cmd) > { > kernel_restart_prepare(cmd); > + disable_nonboot_cpus(); > if (!cmd) > printk(KERN_EMERG "Restarting system.\n"); > else
On 09/04/12 15:36, Andrew Morton wrote: > On Mon, 3 Sep 2012 22:24:58 +0800 > Shawn Guo <shawn.guo@linaro.org> wrote: > >> Like kernel_power_off calls disable_nonboot_cpus, we may want to have >> kernel_restart call disable_nonboot_cpus as well. Doing so can help >> the machines that require boot cpu be the last alive cpu during reboot >> to survive with kernel restart. > That does sound logical. But the changelog is very vague and fluffy. > Does this patch actually fix any known problem on any known machine? > Not to hijack this thread but I have a similar problem that would be partially solved by patch. Basically reboot races with cpu_up and causes a BUG_ON to hit in stop machine. So this patch would fix my problem except for in the case where restart is called from panic (i.e. emergency restart). https://lkml.org/lkml/2012/8/22/3 Here's the commit text: Nothing stops a process from hotplugging in a CPU concurrently with a sys_reboot() call. In such a situation we could have ipi_cpu_stop() mark a cpu as 'offline' and _cpu_up() ignore the fact that the CPU is not really offline and call the CPU_UP_PREPARE notifier. When this happens stop_machine code will complain that the cpu thread already exists and BUG_ON(). CPU0 CPU1 sys_reboot() kernel_restart() machine_restart() machine_shutdown() smp_send_stop() ... ipi_cpu_stop() set_cpu_online(1, false) local_irq_disable() while(1) <PREEMPT> cpu_up() _cpu_up() if (!cpu_online(1)) __cpu_notify(CPU_UP_PREPARE...) cpu_stop_cpu_callback() BUG_ON(stopper->thread) This is easily reproducible by hotplugging in and out in a tight loop while also rebooting. Since the CPU is not really offline and hasn't gone through the proper steps to be marked as such, let's mark the CPU as inactive. This is just as easily testable as online and avoids any possibility of _cpu_up() trying to bring the CPU back online when it never was offline to begin with.
On Tue, Sep 04, 2012 at 03:36:24PM -0700, Andrew Morton wrote: > On Mon, 3 Sep 2012 22:24:58 +0800 > Shawn Guo <shawn.guo@linaro.org> wrote: > > > Like kernel_power_off calls disable_nonboot_cpus, we may want to have > > kernel_restart call disable_nonboot_cpus as well. Doing so can help > > the machines that require boot cpu be the last alive cpu during reboot > > to survive with kernel restart. > > That does sound logical. But the changelog is very vague and fluffy. > Does this patch actually fix any known problem on any known machine? > Yes, it fixes one reboot issue seen on imx6q (Cortex-A9 Quad). The machine requires the restart routine run on primary cpu than secondary ones. Otherwise, the secondary core running restart routine will fail to come to online after reboot.
diff --git a/kernel/sys.c b/kernel/sys.c index 241507f..6fab59a 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -368,6 +368,7 @@ EXPORT_SYMBOL(unregister_reboot_notifier); void kernel_restart(char *cmd) { kernel_restart_prepare(cmd); + disable_nonboot_cpus(); if (!cmd) printk(KERN_EMERG "Restarting system.\n"); else
Like kernel_power_off calls disable_nonboot_cpus, we may want to have kernel_restart call disable_nonboot_cpus as well. Doing so can help the machines that require boot cpu be the last alive cpu during reboot to survive with kernel restart. Signed-off-by: Shawn Guo <shawn.guo@linaro.org> --- kernel/sys.c | 1 + 1 files changed, 1 insertions(+), 0 deletions(-)