[PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS

[PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS

[Leonard Crestez]

This option was removed by "make savedefconfig" in
commit c5054a98bce4 ("ARM: imx_v6_v7_defconfig: Select SMSC_PHY")

This happened because CONFIG_DEBUG_FS was implicitly selected by
CONFIG_TREE_RCU_TRACE which defaulted to true because CONFIG_RCU_TRACE
was enabled by default by commit 961518259b3b ("rcu: Enable RCU
tracepoints by default to aid in debugging")

Recently however CONFIG_RCU_TRACE was completely removed by
commit 6e74c237c410 ("rcu: Remove debugfs tracing")

The result is that imx_v6_v7_defconfig no longer includes DEBUG_FS on
linux-next since next-20170517. This is bad, DEBUG_FS is extremely
useful for kernel introspection and testing.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
---

Patch is against next-20170526. Applying it to shawnguo/imx/defconfig
and cycling via savedefconfig makes this diff go away.

Alternatively maybe DEBUG_FS itself could be made "default y if DEBUG_KERNEL"
or similar?

 arch/arm/configs/imx_v6_v7_defconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/configs/imx_v6_v7_defconfig b/arch/arm/configs/imx_v6_v7_defconfig
index bf1e7e3..51ca814 100644
--- a/arch/arm/configs/imx_v6_v7_defconfig
+++ b/arch/arm/configs/imx_v6_v7_defconfig
@@ -381,6 +381,7 @@ CONFIG_NLS_ISO8859_1=y
 CONFIG_NLS_ISO8859_15=m
 CONFIG_NLS_UTF8=y
 CONFIG_PRINTK_TIME=y
+CONFIG_DEBUG_FS=y
 CONFIG_MAGIC_SYSRQ=y
 # CONFIG_SCHED_DEBUG is not set
 CONFIG_PROVE_LOCKING=y
-- 
2.7.4

[PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS

[Paul E. McKenney]

On Fri, May 26, 2017 at 02:26:06PM +0300, Leonard Crestez wrote:
> This option was removed by "make savedefconfig" in
> commit c5054a98bce4 ("ARM: imx_v6_v7_defconfig: Select SMSC_PHY")
> 
> This happened because CONFIG_DEBUG_FS was implicitly selected by
> CONFIG_TREE_RCU_TRACE which defaulted to true because CONFIG_RCU_TRACE
> was enabled by default by commit 961518259b3b ("rcu: Enable RCU
> tracepoints by default to aid in debugging")
> 
> Recently however CONFIG_RCU_TRACE was completely removed by
> commit 6e74c237c410 ("rcu: Remove debugfs tracing")

CONFIG_RCU_TRACE is still very much alive in its new home at
kernel/rcu/Kconfig.debug:

config RCU_TRACE
	bool "Enable tracing for RCU"
	depends on DEBUG_KERNEL
	default y if TREE_RCU
	select TRACE_CLOCK
	help
	  This option enables additional tracepoints for ftrace-style
	  event tracing.

	  Say Y here if you want to enable RCU tracing
	  Say N if you are unsure.

That said, I need to make it default to "y" if PREEMPT_RCU as well as
the current TREE_RCU.  Would that help?

							Thanx, Paul

> The result is that imx_v6_v7_defconfig no longer includes DEBUG_FS on
> linux-next since next-20170517. This is bad, DEBUG_FS is extremely
> useful for kernel introspection and testing.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> ---
> 
> Patch is against next-20170526. Applying it to shawnguo/imx/defconfig
> and cycling via savedefconfig makes this diff go away.
> 
> Alternatively maybe DEBUG_FS itself could be made "default y if DEBUG_KERNEL"
> or similar?
> 
>  arch/arm/configs/imx_v6_v7_defconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/configs/imx_v6_v7_defconfig b/arch/arm/configs/imx_v6_v7_defconfig
> index bf1e7e3..51ca814 100644
> --- a/arch/arm/configs/imx_v6_v7_defconfig
> +++ b/arch/arm/configs/imx_v6_v7_defconfig
> @@ -381,6 +381,7 @@ CONFIG_NLS_ISO8859_1=y
>  CONFIG_NLS_ISO8859_15=m
>  CONFIG_NLS_UTF8=y
>  CONFIG_PRINTK_TIME=y
> +CONFIG_DEBUG_FS=y
>  CONFIG_MAGIC_SYSRQ=y
>  # CONFIG_SCHED_DEBUG is not set
>  CONFIG_PROVE_LOCKING=y
> -- 
> 2.7.4
> 

[PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS

[Leonard Crestez]

On Fri, 2017-05-26 at 08:42 -0700, Paul E. McKenney wrote:
> On Fri, May 26, 2017 at 02:26:06PM +0300, Leonard Crestez wrote:
> > 
> > This option was removed by "make savedefconfig" in
> > commit c5054a98bce4 ("ARM: imx_v6_v7_defconfig: Select SMSC_PHY")
> > 
> > This happened because CONFIG_DEBUG_FS was implicitly selected by
> > CONFIG_TREE_RCU_TRACE which defaulted to true because CONFIG_RCU_TRACE
> > was enabled by default by commit 961518259b3b ("rcu: Enable RCU
> > tracepoints by default to aid in debugging")
> > 
> > Recently however CONFIG_RCU_TRACE was completely removed by
> > commit 6e74c237c410 ("rcu: Remove debugfs tracing")

> CONFIG_RCU_TRACE is still very much alive in its new home at
> kernel/rcu/Kconfig.debug:

Sorry, what was removed is the dependency on DEBUG_FS. In particular
this snippet:

diff --git a/init/Kconfig b/init/Kconfig
index 2aa14ff..3025383 100644
--
- a/init/Kconfig
+++ b/init/Kconfig
@@ -659,14 +659,6 @@ config
RCU_FAST_NO_HZ
?
??????????Say N if you are unsure.
?
-config
TREE_RCU_TRACE
-???????def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
-???????select DEBUG_FS
-???????help
-?????????This option provides
tracing for the TREE_RCU and
-?????????PREEMPT_RCU implementations,
permitting Makefile to
-?????????trivially select
kernel/rcutree_trace.c.
-
?config RCU_BOOST
????????bool "Enable RCU
priority boosting"
????????depends on RT_MUTEXES && PREEMPT_RCU &&
RCU_EXPERT

> config RCU_TRACE
> 	bool "Enable tracing for RCU"
> 	depends on DEBUG_KERNEL
> 	default y if TREE_RCU
> 	select TRACE_CLOCK
> 	help
> 	??This option enables additional tracepoints for ftrace-style
> 	??event tracing.
> 
> 	??Say Y here if you want to enable RCU tracing
> 	??Say N if you are unsure.
> 
> That said, I need to make it default to "y" if PREEMPT_RCU as well as
> the current TREE_RCU.??Would that help?

I don't think you can help unless you want to make RCU_TRACE depend on
DEBUG_FS for no reason. The proper fix is to have DEBUG_FS inside the
imx_v6_v7_defconfig.

My problem is just an unfortunate accident with default dependencies
and overzealous savedefconfig.

As far as I understand after recent changes RCU_TRACE is now only
useful with tracepoints. Shouldn't it depend on TRACEPOINTS in some
way? It's still possible to compile with RCU_TRACE on and TRACEPOINTS
off, is this intentional? It seems that when this happens you're just
relying on tracepoint macros to expand to nothing.

Fr example maybe RCU_TRACE should be "default y if (TREE_RCU &&
TRACEPOINTS); depends on TRACEPOINTS"?

In theory you could also "select TRACEPOINTS" but then you would end up
enabling TRACEPOINTS by default in all configurations that use TREE_RCU
but don't explicitly disable RCU_TRACE.

I'd say that if $SUBSYSTEM_DEBUG depends on $MAJOR_DEBUG_FEATURE it
should try to avoid selecting $MAJOR_DEBUG_FEATURE by default if it's
not otherwise enabled. As far as I can tell this is how RCU ended up
indirectly pulling in DEBUG_FS and later unexpectedly removed it.

Or I could be completely wrong, kconfig can be very confusing.

--?
Regards,
Leonard

[PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS

[Paul E. McKenney]

On Mon, May 29, 2017 at 02:58:36PM +0300, Leonard Crestez wrote:
> On Fri, 2017-05-26 at 08:42 -0700, Paul E. McKenney wrote:
> > On Fri, May 26, 2017 at 02:26:06PM +0300, Leonard Crestez wrote:
> > > 
> > > This option was removed by "make savedefconfig" in
> > > commit c5054a98bce4 ("ARM: imx_v6_v7_defconfig: Select SMSC_PHY")
> > > 
> > > This happened because CONFIG_DEBUG_FS was implicitly selected by
> > > CONFIG_TREE_RCU_TRACE which defaulted to true because CONFIG_RCU_TRACE
> > > was enabled by default by commit 961518259b3b ("rcu: Enable RCU
> > > tracepoints by default to aid in debugging")
> > > 
> > > Recently however CONFIG_RCU_TRACE was completely removed by
> > > commit 6e74c237c410 ("rcu: Remove debugfs tracing")
> 
> > CONFIG_RCU_TRACE is still very much alive in its new home at
> > kernel/rcu/Kconfig.debug:
> 
> Sorry, what was removed is the dependency on DEBUG_FS. In particular
> this snippet:
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 2aa14ff..3025383 100644
> --
> - a/init/Kconfig
> +++ b/init/Kconfig
> @@ -659,14 +659,6 @@ config
> RCU_FAST_NO_HZ
> ?
> ??????????Say N if you are unsure.
> ?
> -config
> TREE_RCU_TRACE
> -???????def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
> -???????select DEBUG_FS

Ah, you are right.  RCU no longer needs DEBUG_FS, so it no longer
selects it.

> -???????help
> -?????????This option provides
> tracing for the TREE_RCU and
> -?????????PREEMPT_RCU implementations,
> permitting Makefile to
> -?????????trivially select
> kernel/rcutree_trace.c.
> -
> ?config RCU_BOOST
> ????????bool "Enable RCU
> priority boosting"
> ????????depends on RT_MUTEXES && PREEMPT_RCU &&
> RCU_EXPERT
> 
> > config RCU_TRACE
> > 	bool "Enable tracing for RCU"
> > 	depends on DEBUG_KERNEL
> > 	default y if TREE_RCU
> > 	select TRACE_CLOCK
> > 	help
> > 	??This option enables additional tracepoints for ftrace-style
> > 	??event tracing.
> > 
> > 	??Say Y here if you want to enable RCU tracing
> > 	??Say N if you are unsure.
> > 
> > That said, I need to make it default to "y" if PREEMPT_RCU as well as
> > the current TREE_RCU.??Would that help?
> 
> I don't think you can help unless you want to make RCU_TRACE depend on
> DEBUG_FS for no reason. The proper fix is to have DEBUG_FS inside the
> imx_v6_v7_defconfig.
> 
> My problem is just an unfortunate accident with default dependencies
> and overzealous savedefconfig.

Right you are!

> As far as I understand after recent changes RCU_TRACE is now only
> useful with tracepoints. Shouldn't it depend on TRACEPOINTS in some
> way? It's still possible to compile with RCU_TRACE on and TRACEPOINTS
> off, is this intentional? It seems that when this happens you're just
> relying on tracepoint macros to expand to nothing.
> 
> Fr example maybe RCU_TRACE should be "default y if (TREE_RCU &&
> TRACEPOINTS); depends on TRACEPOINTS"?
> 
> In theory you could also "select TRACEPOINTS" but then you would end up
> enabling TRACEPOINTS by default in all configurations that use TREE_RCU
> but don't explicitly disable RCU_TRACE.
> 
> I'd say that if $SUBSYSTEM_DEBUG depends on $MAJOR_DEBUG_FEATURE it
> should try to avoid selecting $MAJOR_DEBUG_FEATURE by default if it's
> not otherwise enabled. As far as I can tell this is how RCU ended up
> indirectly pulling in DEBUG_FS and later unexpectedly removed it.
> 
> Or I could be completely wrong, kconfig can be very confusing.

Interesting questions!  I will give them some thought.

Perhaps TRACEPOINTS is accidentally being enabled for me just as
DEBUG_FS was being accidentally enabled for you.  ;-)

							Thanx, Paul

[PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS

[Shawn Guo]

On Fri, May 26, 2017 at 02:26:06PM +0300, Leonard Crestez wrote:
> This option was removed by "make savedefconfig" in
> commit c5054a98bce4 ("ARM: imx_v6_v7_defconfig: Select SMSC_PHY")
> 
> This happened because CONFIG_DEBUG_FS was implicitly selected by
> CONFIG_TREE_RCU_TRACE which defaulted to true because CONFIG_RCU_TRACE
> was enabled by default by commit 961518259b3b ("rcu: Enable RCU
> tracepoints by default to aid in debugging")
> 
> Recently however CONFIG_RCU_TRACE was completely removed by
> commit 6e74c237c410 ("rcu: Remove debugfs tracing")
> 
> The result is that imx_v6_v7_defconfig no longer includes DEBUG_FS on
> linux-next since next-20170517. This is bad, DEBUG_FS is extremely
> useful for kernel introspection and testing.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>

Applied, thanks.