lkml.org 
[lkml]   [2018]   [Jul]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] ARM64: smp: Fix cpu_up() racing with sys_reboot
On Thu, Jul 19, 2018 at 03:18:46PM -0700, Venkata Narendra Kumar Gutta wrote:
> 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. Based on the similar patchset by for arm
> targets 040c163( "ARM: smp: Fix cpu_up() racing with sys_reboot)"

You really need to use 12 digit commit IDs to refer to commits to
avoid:

$ git log 040c163
fatal: ambiguous argument '040c163': unknown revision or path not in the working tree.

because 7 digits are just too short and given the size of the kernel,
result in conflicting references.

I can find no trace of "040c163" touching arch/arm/kernel/smp.c,
nor can I find a commit with "racing with sys_reboot" touching the
same file.

The commit you reference doesn't seem to be in mainline.

--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 13.8Mbps down 630kbps up
According to speedtest.net: 13Mbps down 490kbps up

\
 
 \ /
  Last update: 2018-07-20 00:56    [W:0.044 / U:0.740 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site