[PATCH REPOST] ARM: smp: Move clear_tasks_mm_cpumask() call to __cpu_die()

[Russell King - ARM Linux]

On Fri, May 04, 2018 at 01:29:39PM +0200, Sebastian Andrzej Siewior wrote:
> From: Grygorii Strashko <grygorii.strashko at ti.com>
> 
> Suspending a CPU on a RT kernel results in the following backtrace:
> 
> | Disabling non-boot CPUs ...
> | BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
> | in_atomic(): 1, irqs_disabled(): 128, pid: 18, name: migration/1
> | INFO: lockdep is turned off.
> | irq event stamp: 122
> | hardirqs last  enabled at (121): [<c06ac0ac>] _raw_spin_unlock_irqrestore+0x88/0x90
> | hardirqs last disabled at (122): [<c06abed0>] _raw_spin_lock_irq+0x28/0x5c
> |  CPU: 1 PID: 18 Comm: migration/1 Tainted: G        W       4.1.4-rt3-01046-g96ac8da #204
> | Hardware name: Generic DRA74X (Flattened Device Tree)
> | [<c0019134>] (unwind_backtrace) from [<c0014774>] (show_stack+0x20/0x24)
> | [<c0014774>] (show_stack) from [<c06a70f4>] (dump_stack+0x88/0xdc)
> | [<c06a70f4>] (dump_stack) from [<c006cab8>] (___might_sleep+0x198/0x2a8)
> | [<c006cab8>] (___might_sleep) from [<c06ac4dc>] (rt_spin_lock+0x30/0x70)
> | [<c06ac4dc>] (rt_spin_lock) from [<c013f790>] (find_lock_task_mm+0x9c/0x174)
> | [<c013f790>] (find_lock_task_mm) from [<c00409ac>] (clear_tasks_mm_cpumask+0xb4/0x1ac)
> | [<c00409ac>] (clear_tasks_mm_cpumask) from [<c00166a4>] (__cpu_disable+0x98/0xbc)
> | [<c00166a4>] (__cpu_disable) from [<c06a2e8c>] (take_cpu_down+0x1c/0x50)
> | [<c06a2e8c>] (take_cpu_down) from [<c00f2600>] (multi_cpu_stop+0x11c/0x158)
> | [<c00f2600>] (multi_cpu_stop) from [<c00f2a9c>] (cpu_stopper_thread+0xc4/0x184)
> | [<c00f2a9c>] (cpu_stopper_thread) from [<c0069058>] (smpboot_thread_fn+0x18c/0x324)
> | [<c0069058>] (smpboot_thread_fn) from [<c00649c4>] (kthread+0xe8/0x104)
> | [<c00649c4>] (kthread) from [<c0010058>] (ret_from_fork+0x14/0x3c)
> | CPU1: shutdown
> 
> The root cause of above backtrace is task_lock() which takes a sleeping
> lock on -RT.
> 
> To fix the issue, move clear_tasks_mm_cpumask() call from __cpu_disable()
> to __cpu_die() which is called on the thread which is asking for a target
> CPU to be shutdown. In addition, this change restores CPU hotplug
> functionality on ARM CPU1 can be unplugged/plugged many times.

This looks fine to me - all the paths that use the mm_cpumask() check
that the CPU is still marked online.

Please send to the patch system, thanks.

> 
> Signed-off-by: Grygorii Strashko <grygorii.strashko at ti.com>
> Cc: <linux-arm-kernel at lists.infradead.org>
> Cc: Sekhar Nori <nsekhar at ti.com>
> Cc: Russell King <linux at arm.linux.org.uk>
> Link: http://lkml.kernel.org/r/1441995683-30817-1-git-send-email-grygorii.strashko@ti.com
> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
> [bigeasy: slighty edited the commit message]
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
> ---
>  arch/arm/kernel/smp.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -236,8 +236,6 @@ int __cpu_disable(void)
>  	flush_cache_louis();
>  	local_flush_tlb_all();
>  
> -	clear_tasks_mm_cpumask(cpu);
> -
>  	return 0;
>  }
>  
> @@ -255,6 +253,7 @@ void __cpu_die(unsigned int cpu)
>  	}
>  	pr_debug("CPU%u: shutdown\n", cpu);
>  
> +	clear_tasks_mm_cpumask(cpu);
>  	/*
>  	 * platform_cpu_kill() is generally expected to do the powering off
>  	 * and/or cutting of clocks to the dying CPU.  Optionally, this may

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up
According to speedtest.net: 8.21Mbps down 510kbps up