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

Hi guys,

On Fri, May 30, 2014 at 08:08:38PM +0100, Kevin Hilman wrote:

Will Deacon [off-list ref] writes:

quoted

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