Messages in this thread | | | Date | Mon, 29 May 2017 08:11:00 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS |
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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
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