[PATCH RT 01/10] ARM: smp: Move clear_tasks_mm_cpumask() call to __cpu_die()

From: Steven Rostedt
Date: Fri Feb 26 2016 - 17:19:58 EST

3.10.97-rt106-rc1 stable review patch.
If anyone has any objections, please let me know.


From: Grygorii Strashko <grygorii.strashko@xxxxxx>

When running with the RT-kernel (4.1.5-rt5) on TI OMAP dra7-evm and trying
to do Suspend to RAM, the following backtrace occurs:

Disabling non-boot CPUs ...
PM: noirq suspend of devices complete after 7.295 msecs
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
softirqs last enabled at (0): [<c003d294>] copy_process.part.52+0x410/0x19d8
softirqs last disabled at (0): [< (null)>] (null)
Preemption disabled at:[< (null)>] (null)
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
PM: Calling sched_clock_suspend+0x0/0x40
PM: Calling timekeeping_suspend+0x0/0x2e0
PM: Calling irq_gc_suspend+0x0/0x68
PM: Calling fw_suspend+0x0/0x2c
PM: Calling cpu_pm_suspend+0x0/0x28

Also, sometimes system stucks right after displaying "Disabling non-boot
CPUs ...". 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 CPUhotplug functionality
on TI OMAP dra7-evm and CPU1 can be unplugged/plugged many times.

Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Sekhar Nori <nsekhar@xxxxxx>
Cc: Austin Schuh <austin@xxxxxxxxxxxxxxxx>
Cc: <philipp@xxxxxxxxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
Cc: <bigeasy@xxxxxxxxxxxxx>
Cc: stable-rt@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1441995683-30817-1-git-send-email-grygorii.strashko@xxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
arch/arm/kernel/smp.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 5919eb451bb9..7ad24aa57040 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -192,8 +192,6 @@ int __cpuinit __cpu_disable(void)

- clear_tasks_mm_cpumask(cpu);
return 0;

@@ -209,6 +207,9 @@ void __cpuinit __cpu_die(unsigned int cpu)
pr_err("CPU%u: cpu didn't die\n", cpu);
+ clear_tasks_mm_cpumask(cpu);
printk(KERN_NOTICE "CPU%u: shutdown\n", cpu);