rcu: Detect illegal rcu dereference in extended quiescent state

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.

Uses of RCU from within dyntick-idle mode are totally ignored by
RCU, hence the importance of these checks.

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>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 8d7efc8a062f34fa980e777a49e7a12501e0a4ad..7d8fa7cd32bc6b2f2df07bce4b2bf2a4b1940271 100644 (file)
--- 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 5031cafb6f8a3b108c6b7541285669ff488a6b40..e4d8a986c095151e0216cb0e42d9656c5d3c02ce 100644 (file)
--- 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 da775c87f27f6aa146bf9b929f72fe0e386d8b41..9e493b9f615f7d70e8263d3c9c6be6b0a7baf23e 100644 (file)
--- 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 f0a94324032b85b6bac023de7829e691168d7c62..c9b4adfc3e36d2a8790018812fb78ebeddf3400a 100644 (file)
--- 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
 
 /*