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Subject[PATCH tip/core/rcu 49/55] rcu: Detect illegal rcu dereference in extended quiescent state
Date
From: Frederic Weisbecker <fweisbec@gmail.com>

Report that none of the rcu read lock maps are held while in an RCU
extended quiescent state (in this case, the RCU extended quiescent state
is dyntick-idle mode). This helps detect any use of rcu_dereference()
and friends from within dyntick-idle mode.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 36 ++++++++++++++++++++++++++++++++++++
kernel/rcupdate.c | 17 ++++++++++++++++-
kernel/rcutiny.c | 14 ++++++++++++++
kernel/rcutree.c | 16 ++++++++++++++++
4 files changed, 82 insertions(+), 1 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 8d7efc8..7d8fa7c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -231,6 +231,14 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */

+
+#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_NO_HZ)
+extern bool rcu_check_extended_qs(void);
+#else
+static inline bool rcu_check_extended_qs(void) { return false; }
+#endif
+
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC

#define PROVE_RCU(a) a
@@ -264,11 +272,25 @@ extern int debug_lockdep_rcu_enabled(void);
*
* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
+ *
+ * Note that if the CPU is in an extended quiescent state, for example,
+ * if the CPU is in dyntick-idle mode, then rcu_read_lock_held() returns
+ * false even if the CPU did an rcu_read_lock(). The reason for this is
+ * that RCU ignores CPUs that are in extended quiescent states, so such
+ * a CPU is effectively never in an RCU read-side critical section
+ * regardless of what RCU primitives it invokes. This state of affairs
+ * is required -- RCU would otherwise need to periodically wake up
+ * dyntick-idle CPUs, which would defeat the whole purpose of dyntick-idle
+ * mode.
*/
static inline int rcu_read_lock_held(void)
{
if (!debug_lockdep_rcu_enabled())
return 1;
+
+ if (rcu_check_extended_qs())
+ return 0;
+
return lock_is_held(&rcu_lock_map);
}

@@ -292,6 +314,16 @@ extern int rcu_read_lock_bh_held(void);
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
+ *
+ * Note that if the CPU is in an extended quiescent state, for example,
+ * if the CPU is in dyntick-idle mode, then rcu_read_lock_held() returns
+ * false even if the CPU did an rcu_read_lock(). The reason for this is
+ * that RCU ignores CPUs that are in extended quiescent states, so such
+ * a CPU is effectively never in an RCU read-side critical section
+ * regardless of what RCU primitives it invokes. This state of affairs
+ * is required -- RCU would otherwise need to periodically wake up
+ * dyntick-idle CPUs, which would defeat the whole purpose of dyntick-idle
+ * mode.
*/
#ifdef CONFIG_PREEMPT
static inline int rcu_read_lock_sched_held(void)
@@ -300,6 +332,10 @@ static inline int rcu_read_lock_sched_held(void)

if (!debug_lockdep_rcu_enabled())
return 1;
+
+ if (rcu_check_extended_qs())
+ return 0;
+
if (debug_locks)
lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 5031caf..e4d8a98 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -87,12 +87,27 @@ EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
* that require that they be called within an RCU read-side critical
* section.
*
- * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
+ * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
+ * and while lockdep is disabled.
+ *
+ * Note that if the CPU is in an extended quiescent state, for example,
+ * if the CPU is in dyntick-idle mode, then rcu_read_lock_held() returns
+ * false even if the CPU did an rcu_read_lock(). The reason for this is
+ * that RCU ignores CPUs that are in extended quiescent states, so such
+ * a CPU is effectively never in an RCU read-side critical section
+ * regardless of what RCU primitives it invokes. This state of affairs
+ * is required -- RCU would otherwise need to periodically wake up
+ * dyntick-idle CPUs, which would defeat the whole purpose of dyntick-idle
+ * mode.
*/
int rcu_read_lock_bh_held(void)
{
if (!debug_lockdep_rcu_enabled())
return 1;
+
+ if (rcu_check_extended_qs())
+ return 0;
+
return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index da775c8..9e493b9 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -78,6 +78,20 @@ void rcu_exit_nohz(void)
rcu_dynticks_nesting++;
}

+
+#ifdef CONFIG_PROVE_RCU
+
+bool rcu_check_extended_qs(void)
+{
+ if (!rcu_dynticks_nesting)
+ return true;
+
+ return false;
+}
+EXPORT_SYMBOL_GPL(rcu_check_extended_qs);
+
+#endif
+
#endif /* #ifdef CONFIG_NO_HZ */

/*
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f0a9432..c9b4adf 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -465,6 +465,22 @@ void rcu_irq_exit(void)
rcu_enter_nohz();
}

+#ifdef CONFIG_PROVE_RCU
+
+bool rcu_check_extended_qs(void)
+{
+ struct rcu_dynticks *rdtp;
+
+ rdtp = &per_cpu(rcu_dynticks, raw_smp_processor_id());
+ if (atomic_read(&rdtp->dynticks) & 0x1)
+ return false;
+
+ return true;
+}
+EXPORT_SYMBOL_GPL(rcu_check_extended_qs);
+
+#endif /* CONFIG_PROVE_RCU */
+
#ifdef CONFIG_SMP

/*
--
1.7.3.2


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