[PATCH v6 2/2] arm64: enable context tracking

[will.deacon@arm.com (Will Deacon)]

Hi guys,

On Fri, May 30, 2014 at 08:08:38PM +0100, Kevin Hilman wrote:
> Will Deacon <will.deacon@arm.com> writes:
> > I'd like to give these some stress testing before it gets merged, so I'm
> > not sure if it'll make it for 3.16 given where we are at the moment.
> 
> FWIW, this feature is disabled by default.  I use the following kconfig
> fragment to enable the various parts I use for testing:
> 
> CONFIG_NO_HZ=y
> CONFIG_NO_HZ_FULL=y
> CONFIG_NO_HZ_FULL_ALL=y
> CONFIG_NO_HZ_FULL_SYSIDLE=y
> 
> # default to power-efficient workqueues (which are then set to unbound)
> CONFIG_WQ_POWER_EFFICIENT_DEFAULT=y
> 
> # lockup detector sets a 4s timer on every CPU, which wakes CPUs
> # from idle. (alternately, can be controlled via procfs,
> # e.g: echo 0 > /proc/sys/kernel/watchdog)
> #CONFIG_LOCKUP_DETECTOR=n

I had a go with this, but I couldn't seem to trigger any context tracking
without forcing CONFIG_CONTEXT_TRACKING_FORCE=y. Does that mean we're
missing something else?

Anyway, with that forced on, I see the following during boot:


------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:418 rcu_eqs_enter+0x84/0xa4()
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.15.0-rc8+ #5
Call trace:
[<ffffffc000088048>] dump_backtrace+0x0/0x130
[<ffffffc000088188>] show_stack+0x10/0x1c
[<ffffffc0004891a0>] dump_stack+0x74/0xbc
[<ffffffc0000a45e0>] warn_slowpath_common+0x8c/0xb4
[<ffffffc0000a46cc>] warn_slowpath_null+0x14/0x20
[<ffffffc0000efc14>] rcu_eqs_enter+0x80/0xa4
[<ffffffc0000efc58>] rcu_idle_enter+0x20/0x50
[<ffffffc0000dd314>] cpu_startup_entry+0x118/0x184
[<ffffffc0004865ec>] rest_init+0x7c/0x88
[<ffffffc000609800>] start_kernel+0x368/0x37c
---[ end trace c17313e162496e65 ]---
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:541 rcu_eqs_exit+0xb0/0xbc()
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W     3.15.0-rc8+ #5
Call trace:
[<ffffffc000088048>] dump_backtrace+0x0/0x130
[<ffffffc000088188>] show_stack+0x10/0x1c
[<ffffffc0004891a0>] dump_stack+0x74/0xbc
[<ffffffc0000a45e0>] warn_slowpath_common+0x8c/0xb4
[<ffffffc0000a46cc>] warn_slowpath_null+0x14/0x20
[<ffffffc0000ed384>] rcu_eqs_exit+0xac/0xbc
[<ffffffc0000efdac>] rcu_user_exit+0xc/0x18
[<ffffffc00011d48c>] context_tracking_user_exit+0xc4/0xd4
[<ffffffc000083d98>] el1_irq+0x58/0xd4
[<ffffffc0000dd318>] cpu_startup_entry+0x11c/0x184
[<ffffffc0004865ec>] rest_init+0x7c/0x88
[<ffffffc000609800>] start_kernel+0x368/0x37c
---[ end trace c17313e162496e66 ]---


Can you take a look please? I had to fix up some conflicts to apply your
patches against our for-next branch, so I've put a branch here for you to
look at:

  git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git aarch64/context-tracking

Cheers,

Will