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Date: Wed, 11 May 2011 13:18:52 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Yinghai Lu <yinghai@...nel.org>
Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40
On Wed, May 11, 2011 at 09:56:35AM -0700, Yinghai Lu wrote:
> On Tue, May 10, 2011 at 9:54 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Tue, May 10, 2011 at 01:52:52PM -0700, Yinghai Lu wrote:
> >> On 05/10/2011 12:32 PM, Paul E. McKenney wrote:
> >> > On Tue, May 10, 2011 at 11:04:57AM -0700, Yinghai Lu wrote:
> >> >> On 05/10/2011 01:56 AM, Paul E. McKenney wrote:
> >> >>> On Mon, May 09, 2011 at 02:09:21PM -0700, Yinghai Lu wrote:
> >> >>>> On Mon, May 9, 2011 at 12:36 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >> >>>>>
> >> >>>>> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> >> >>>>>
> >> >>>>>> Hello, Ingo,
> >> >>>>>>
> >> >>>>>> This pull request covers RCU chnages for 2.6.40. The major new features
> >> >>>>>> are RCU priority boosting and the addition of kfree_rcu(), the latter
> >> >>>>>> courtesy of Lai Jiangshan. These two features cover well over half
> >> >>>>>> of the commits. There are a number of smaller features and bug fixes.
> >> >>>>>> All have been sent to LKML in the following batches:
> >> >>>>>>
> >> >>>>>> 0. https://lkml.org/lkml/2011/2/22/660: RCU priority boosting preview
> >> >>>>>> 1. https://lkml.org/lkml/2011/5/1/19: RCU priority boosting, kfree_rcu()
> >> >>>>>> 2. https://lkml.org/lkml/2011/5/2/40: More uses of kfree_rcu()
> >> >>>>>> 3. https://lkml.org/lkml/2011/5/8/60: miscellaneous
> >> >>>>>>
> >> >>>>>> The kfree_rcu() uses in the pull request have Acked-by:s from the
> >> >>>>>> maintainers. I have some additional kfree_rcu() requests that lack
> >> >>>>>> Acked-by:s, and I will deal with these later.
> >> >>>>>>
> >> >>>>>> These channges are available in the -rcu git repository at:
> >> >>>>>>
> >> >>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/next
> >> >>>>>
> >> >>>>> Pulled, thanks a lot Paul!
> >> >>>>>
> >> >>>>
> >> >>>> it seems with this one in tip, my 8 sockets test setup will report cpu stall.
> >> >>>>
> >> >>>> after hard code to enable rcu_cpu_stall_suppress
> >> >>>>
> >> >>>> Index: linux-2.6/kernel/rcutree.c
> >> >>>> ===================================================================
> >> >>>> --- linux-2.6.orig/kernel/rcutree.c
> >> >>>> +++ linux-2.6/kernel/rcutree.c
> >> >>>> @@ -174,7 +174,7 @@ module_param(blimit, int, 0);
> >> >>>> module_param(qhimark, int, 0);
> >> >>>> module_param(qlowmark, int, 0);
> >> >>>>
> >> >>>> -int rcu_cpu_stall_suppress __read_mostly;
> >> >>>> +int rcu_cpu_stall_suppress __read_mostly = 1;
> >> >>>> module_param(rcu_cpu_stall_suppress, int, 0644);
> >> >>>>
> >> >>>> static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
> >> >>>>
> >> >>>> will get system hang after pnp ACPI init.
> >> >>>
> >> >>> Could you please send the stack traces from the RCU CPU stall? Also,
> >> >>> you do have ce31332d3c77532d6ea97ddcb475a2b02dd358b4 applied, correct?
> >> >>>
> >> >>> Thanx, Paul
> >> >>
> >> >> Do not have time to bisect it at this point.
> >> >
> >> > Could you please send the stack traces from the RCU CPU stall?
> >
> > Thank you! OK, so CPU 0 has not been responding, despite resched IPIs.
> > Everyone is idle, except for CPU 124, which detected the stall, and
> > possibly CPU 0, which has csum_partial_copy_generic() on the stack, though
> > that looks like a backtrace error to me. The fact that it hangs if you
> > disable RCU CPU stall detection leads me to believe that something real
> > is being detected.
>
> the problem is that now I can not disable RCU CPU stall detection any more.
There is a rcu_cpu_stall_suppress module parameter, and you should be
able to pass in rcu_cpu_stall_suppress=1 as a boot parameter. However,
I did produce a patch that reverts the change, please see below.
I would be surprised if this did anything different than your change
that initializes rcu_cpu_stall_suppress to 1. If this patch somehow
does make a difference, please let me know.
Thanx, Paul
------------------------------------------------------------------------
diff --git a/Documentation/RCU/00-INDEX b/Documentation/RCU/00-INDEX
index 1d7a885..71b6f50 100644
--- a/Documentation/RCU/00-INDEX
+++ b/Documentation/RCU/00-INDEX
@@ -21,7 +21,7 @@ rcu.txt
RTFP.txt
- List of RCU papers (bibliography) going back to 1980.
stallwarn.txt
- - RCU CPU stall warnings (module parameter rcu_cpu_stall_suppress)
+ - RCU CPU stall warnings (CONFIG_RCU_CPU_STALL_DETECTOR)
torture.txt
- RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST)
trace.txt
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 4e95920..862c08e 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -1,25 +1,22 @@
Using RCU's CPU Stall Detector
-The rcu_cpu_stall_suppress module parameter enables RCU's CPU stall
-detector, which detects conditions that unduly delay RCU grace periods.
-This module parameter enables CPU stall detection by default, but
-may be overridden via boot-time parameter or at runtime via sysfs.
-The stall detector's idea of what constitutes "unduly delayed" is
-controlled by a set of kernel configuration variables and cpp macros:
+The CONFIG_RCU_CPU_STALL_DETECTOR kernel config parameter enables
+RCU's CPU stall detector, which detects conditions that unduly delay
+RCU grace periods. The stall detector's idea of what constitutes
+"unduly delayed" is controlled by a set of C preprocessor macros:
-CONFIG_RCU_CPU_STALL_TIMEOUT
+RCU_SECONDS_TILL_STALL_CHECK
- This kernel configuration parameter defines the period of time
- that RCU will wait from the beginning of a grace period until it
- issues an RCU CPU stall warning. This time period is normally
- ten seconds.
+ This macro defines the period of time that RCU will wait from
+ the beginning of a grace period until it issues an RCU CPU
+ stall warning. This time period is normally ten seconds.
RCU_SECONDS_TILL_STALL_RECHECK
This macro defines the period of time that RCU will wait after
issuing a stall warning until it issues another stall warning
- for the same stall. This time period is normally set to three
- times the check interval plus thirty seconds.
+ for the same stall. This time period is normally set to thirty
+ seconds.
RCU_STALL_RAT_DELAY
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 86f44a3..2e8fbed 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -174,8 +174,10 @@ module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);
-int rcu_cpu_stall_suppress __read_mostly;
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+int rcu_cpu_stall_suppress __read_mostly = RCU_CPU_STALL_SUPPRESS_INIT;
module_param(rcu_cpu_stall_suppress, int, 0644);
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
static int rcu_pending(int cpu);
@@ -497,6 +499,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
#endif /* #else #ifdef CONFIG_NO_HZ */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+
int rcu_cpu_stall_suppress __read_mostly;
static void record_gp_stall_check_time(struct rcu_state *rsp)
@@ -635,6 +639,26 @@ static void __init check_cpu_stall_init(void)
atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
}
+#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+
+static void record_gp_stall_check_time(struct rcu_state *rsp)
+{
+}
+
+static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
+{
+}
+
+void rcu_cpu_stall_reset(void)
+{
+}
+
+static void __init check_cpu_stall_init(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+
/*
* Update CPU-local rcu_data state to record the newly noticed grace period.
* This is used both when we started the grace period and when we notice
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 93d4a1c..c8e5bf4 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -317,6 +317,7 @@ struct rcu_data {
#endif /* #else #ifdef CONFIG_NO_HZ */
#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
#ifdef CONFIG_PROVE_RCU
#define RCU_STALL_DELAY_DELTA (5 * HZ)
@@ -334,6 +335,13 @@ struct rcu_data {
/* scheduling clock irq */
/* before ratting on them. */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE
+#define RCU_CPU_STALL_SUPPRESS_INIT 0
+#else
+#define RCU_CPU_STALL_SUPPRESS_INIT 1
+#endif
+
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
/*
* RCU global state, including node hierarchy. This hierarchy is
@@ -382,8 +390,10 @@ struct rcu_state {
/* due to no GP active. */
unsigned long gp_start; /* Time at which GP started, */
/* but in jiffies. */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
unsigned long jiffies_stall; /* Time at which to check */
/* for CPU stalls. */
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
unsigned long gp_max; /* Maximum GP duration in */
/* jiffies. */
char *name; /* Name of structure. */
@@ -421,9 +431,11 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
unsigned long flags);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
static void rcu_print_detail_task_stall(struct rcu_state *rsp);
static void rcu_print_task_stall(struct rcu_node *rnp);
static void rcu_preempt_stall_reset(void);
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index ed339702..f77bc10 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -54,6 +54,10 @@ static void __init rcu_bootup_announce_oddness(void)
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
#endif
+#ifndef CONFIG_RCU_CPU_STALL_DETECTOR
+ printk(KERN_INFO
+ "\tRCU-based detection of stalled CPUs is disabled.\n");
+#endif
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n");
#endif
@@ -398,6 +402,8 @@ void __rcu_read_unlock(void)
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+
#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
/*
@@ -466,6 +472,8 @@ static void rcu_preempt_stall_reset(void)
rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
}
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+
/*
* Check that the list of blocked tasks for the newly completed grace
* period is in fact empty. It is a serious bug to complete a grace
@@ -922,6 +930,8 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
@@ -946,6 +956,8 @@ static void rcu_preempt_stall_reset(void)
{
}
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+
/*
* Because there is no preemptible RCU, there can be no readers blocked,
* so there is no need to check for blocked tasks. So check only for
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 3aa2780..a863e35 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -875,9 +875,22 @@ config RCU_TORTURE_TEST_RUNNABLE
Say N here if you want the RCU torture tests to start only
after being manually enabled via /proc.
+config RCU_CPU_STALL_DETECTOR
+ bool "Check for stalled CPUs delaying RCU grace periods"
+ depends on TREE_RCU || TREE_PREEMPT_RCU
+ default y
+ help
+ This option causes RCU to printk information on which
+ CPUs are delaying the current grace period, but only when
+ the grace period extends for excessive time periods.
+
+ Say N if you want to disable such checks.
+
+ Say Y if you are unsure.
+
config RCU_CPU_STALL_TIMEOUT
int "RCU CPU stall timeout in seconds"
- depends on TREE_RCU || TREE_PREEMPT_RCU
+ depends on RCU_CPU_STALL_DETECTOR
range 3 300
default 60
help
@@ -886,9 +899,22 @@ config RCU_CPU_STALL_TIMEOUT
RCU grace period persists, additional CPU stall warnings are
printed at more widely spaced intervals.
+config RCU_CPU_STALL_DETECTOR_RUNNABLE
+ bool "RCU CPU stall checking starts automatically at boot"
+ depends on RCU_CPU_STALL_DETECTOR
+ default y
+ help
+ If set, start checking for RCU CPU stalls immediately on
+ boot. Otherwise, RCU CPU stall checking must be manually
+ enabled.
+
+ Say Y if you are unsure.
+
+ Say N if you wish to suppress RCU CPU stall checking during boot.
+
config RCU_CPU_STALL_VERBOSE
bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"
- depends on TREE_PREEMPT_RCU
+ depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU
default y
help
This option causes RCU to printk detailed per-task information
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