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rcu: Remove CONFIG_RCU_CPU_STALL_INFO
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The CONFIG_RCU_CPU_STALL_INFO has been default-y for a couple of
releases with no complaints, so it is time to eliminate this Kconfig
option entirely, so that the long-form RCU CPU stall warnings cannot
be disabled.  This commit does just that.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Paul E. McKenney committed Jul 17, 2015
1 parent 9b68387 commit 75c27f1
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Showing 16 changed files with 2 additions and 85 deletions.
12 changes: 2 additions & 10 deletions Documentation/RCU/stallwarn.txt
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Expand Up @@ -26,12 +26,6 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
Stall-warning messages may be enabled and disabled completely via
/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.

CONFIG_RCU_CPU_STALL_INFO

This kernel configuration parameter causes the stall warning to
print out additional per-CPU diagnostic information, including
information on scheduling-clock ticks and RCU's idle-CPU tracking.

RCU_STALL_DELAY_DELTA

Although the lockdep facility is extremely useful, it does add
Expand Down Expand Up @@ -101,15 +95,13 @@ interact. Please note that it is not possible to entirely eliminate this
sort of false positive without resorting to things like stop_machine(),
which is overkill for this sort of problem.

If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
more information is printed with the stall-warning message, for example:
Recent kernels will print a long form of the stall-warning message:

INFO: rcu_preempt detected stall on CPU
0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 softirq=82/543
(t=65000 jiffies)

In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is
printed:
In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed:

INFO: rcu_preempt detected stall on CPU
0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D
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4 changes: 0 additions & 4 deletions kernel/rcu/tree.h
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Expand Up @@ -288,12 +288,10 @@ struct rcu_data {
bool gpwrap; /* Possible gpnum/completed wrap. */
struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
unsigned long grpmask; /* Mask to apply to leaf qsmask. */
#ifdef CONFIG_RCU_CPU_STALL_INFO
unsigned long ticks_this_gp; /* The number of scheduling-clock */
/* ticks this CPU has handled */
/* during and after the last grace */
/* period it is aware of. */
#endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

/* 2) batch handling */
/*
Expand Down Expand Up @@ -388,9 +386,7 @@ struct rcu_data {
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */

/* 8) RCU CPU stall data. */
#ifdef CONFIG_RCU_CPU_STALL_INFO
unsigned int softirq_snap; /* Snapshot of softirq activity. */
#endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

int cpu;
struct rcu_state *rsp;
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45 changes: 0 additions & 45 deletions kernel/rcu/tree_plugin.h
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Expand Up @@ -82,8 +82,6 @@ static void __init rcu_bootup_announce_oddness(void)
pr_info("\tRCU lockdep checking is enabled.\n");
if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE))
pr_info("\tRCU torture testing starts during boot.\n");
if (IS_ENABLED(CONFIG_RCU_CPU_STALL_INFO))
pr_info("\tAdditional per-CPU info printed with stalls.\n");
if (RCU_NUM_LVLS >= 4)
pr_info("\tFour(or more)-level hierarchy is enabled.\n");
if (RCU_FANOUT_LEAF != 16)
Expand Down Expand Up @@ -418,8 +416,6 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp)
rcu_print_detail_task_stall_rnp(rnp);
}

#ifdef CONFIG_RCU_CPU_STALL_INFO

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
Expand All @@ -431,18 +427,6 @@ static void rcu_print_task_stall_end(void)
pr_cont("\n");
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}

static void rcu_print_task_stall_end(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
Expand Down Expand Up @@ -1685,8 +1669,6 @@ early_initcall(rcu_register_oom_notifier);

#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
Expand Down Expand Up @@ -1775,33 +1757,6 @@ static void increment_cpu_stall_ticks(void)
raw_cpu_inc(rsp->rda->ticks_this_gp);
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
pr_cont(" {");
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
pr_cont(" %d", cpu);
}

static void print_cpu_stall_info_end(void)
{
pr_cont("} ");
}

static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}

static void increment_cpu_stall_ticks(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

#ifdef CONFIG_RCU_NOCB_CPU

/*
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14 changes: 0 additions & 14 deletions lib/Kconfig.debug
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Expand Up @@ -1353,20 +1353,6 @@ config RCU_CPU_STALL_TIMEOUT
RCU grace period persists, additional CPU stall warnings are
printed at more widely spaced intervals.

config RCU_CPU_STALL_INFO
bool "Print additional diagnostics on RCU CPU stall"
depends on (TREE_RCU || PREEMPT_RCU) && DEBUG_KERNEL
default y
help
For each stalled CPU that is aware of the current RCU grace
period, print out additional per-CPU diagnostic information
regarding scheduling-clock ticks, idle state, and,
for RCU_FAST_NO_HZ kernels, idle-entry state.

Say N if you are unsure.

Say Y if you want to enable such diagnostics.

config RCU_TRACE
bool "Enable tracing for RCU"
depends on DEBUG_KERNEL
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1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE01
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Expand Up @@ -13,7 +13,6 @@ CONFIG_MAXSMP=y
CONFIG_RCU_NOCB_CPU=y
CONFIG_RCU_NOCB_CPU_ZERO=y
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE02
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Expand Up @@ -17,7 +17,6 @@ CONFIG_RCU_FANOUT_LEAF=3
CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE02-T
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Expand Up @@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT_LEAF=3
CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE03
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Expand Up @@ -13,7 +13,6 @@ CONFIG_RCU_FANOUT=2
CONFIG_RCU_FANOUT_LEAF=2
CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=y
CONFIG_RCU_KTHREAD_PRIO=2
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
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1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE04
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Expand Up @@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT=4
CONFIG_RCU_FANOUT_LEAF=4
CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE05
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Expand Up @@ -17,6 +17,5 @@ CONFIG_RCU_NOCB_CPU_NONE=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
#CHECK#CONFIG_PROVE_RCU=y
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE06
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Expand Up @@ -18,6 +18,5 @@ CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
#CHECK#CONFIG_PROVE_RCU=y
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE07
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Expand Up @@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT=2
CONFIG_RCU_FANOUT_LEAF=2
CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE08
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Expand Up @@ -19,7 +19,6 @@ CONFIG_RCU_NOCB_CPU_ALL=y
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_PROVE_LOCKING=y
#CHECK#CONFIG_PROVE_RCU=y
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
CONFIG_RCU_EXPERT=y
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE08-T
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Expand Up @@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT_LEAF=2
CONFIG_RCU_NOCB_CPU=y
CONFIG_RCU_NOCB_CPU_ALL=y
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/configs/rcu/TREE09
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Expand Up @@ -13,7 +13,6 @@ CONFIG_SUSPEND=n
CONFIG_HIBERNATION=n
CONFIG_RCU_NOCB_CPU=n
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_RCU_CPU_STALL_INFO=n
CONFIG_RCU_BOOST=n
CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
#CHECK#CONFIG_RCU_EXPERT=n
1 change: 0 additions & 1 deletion tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
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Expand Up @@ -16,7 +16,6 @@ CONFIG_PROVE_LOCKING -- Do several, covering CONFIG_DEBUG_LOCK_ALLOC=y and not.
CONFIG_PROVE_RCU -- Hardwired to CONFIG_PROVE_LOCKING.
CONFIG_RCU_BOOST -- one of PREEMPT_RCU.
CONFIG_RCU_KTHREAD_PRIO -- set to 2 for _BOOST testing.
CONFIG_RCU_CPU_STALL_INFO -- Now default, avoid at least twice.
CONFIG_RCU_FANOUT -- Cover hierarchy, but overlap with others.
CONFIG_RCU_FANOUT_LEAF -- Do one non-default.
CONFIG_RCU_FAST_NO_HZ -- Do one, but not with CONFIG_RCU_NOCB_CPU_ALL.
Expand Down

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