rcu: Restore checks for blocking in RCU read-side critical sections

Long ago, using TREE_RCU with PREEMPT would result in "scheduling
while atomic" diagnostics if you blocked in an RCU read-side critical
section.  However, PREEMPT now implies TREE_PREEMPT_RCU, which defeats
this diagnostic.  This commit therefore adds a replacement diagnostic
based on PROVE_RCU.

Because rcu_lockdep_assert() and lockdep_rcu_dereference() are now being
used for things that have nothing to do with rcu_dereference(), rename
lockdep_rcu_dereference() to lockdep_rcu_suspicious() and add a third
argument that is a string indicating what is suspicious.  This third
argument is passed in from a new third argument to rcu_lockdep_assert().
Update all calls to rcu_lockdep_assert() to add an informative third
argument.

Also, add a pair of rcu_lockdep_assert() calls from within
rcu_note_context_switch(), one complaining if a context switch occurs
in an RCU-bh read-side critical section and another complaining if a
context switch occurs in an RCU-sched read-side critical section.
These are present only if the PROVE_RCU kernel parameter is enabled.

Finally, fix some checkpatch whitespace complaints in lockdep.c.

Again, you must enable PROVE_RCU to see these new diagnostics.  But you
are enabling PROVE_RCU to check out new RCU uses in any case, aren't you?

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

2 files changed, 23 insertions, 7 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index ef820a3c378b..b6a56e37284c 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -548,7 +548,7 @@ do {									\
 #endif
 
 #ifdef CONFIG_PROVE_RCU
-extern void lockdep_rcu_dereference(const char *file, const int line);
+void lockdep_rcu_suspicious(const char *file, const int line, const char *s);
 #endif
 
 #endif /* __LINUX_LOCKDEP_H */
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 8f4f881a0ad8..8e7470d8b676 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -297,19 +297,31 @@ extern int rcu_my_thread_group_empty(void);
 /**
  * rcu_lockdep_assert - emit lockdep splat if specified condition not met
  * @c: condition to check
+ * @s: informative message
  */
-#define rcu_lockdep_assert(c)                                           \
+#define rcu_lockdep_assert(c, s)                                        \
         do {                                                            \
                 static bool __warned;                                   \
                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
                         __warned = true;                                \
-                        lockdep_rcu_dereference(__FILE__, __LINE__);    \
+                        lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
                 }                                                       \
         } while (0)
 
+#define rcu_sleep_check()                                               \
+        do {                                                            \
+                rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),     \
+                                   "Illegal context switch in RCU-bh"   \
+                                   " read-side critical section");      \
+                rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),  \
+                                   "Illegal context switch in RCU-sched"\
+                                   " read-side critical section");      \
+        } while (0)
+
 #else /* #ifdef CONFIG_PROVE_RCU */
 
-#define rcu_lockdep_assert(c) do { } while (0)
+#define rcu_lockdep_assert(c, s) do { } while (0)
+#define rcu_sleep_check() do { } while (0)
 
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 
@@ -338,14 +350,16 @@ extern int rcu_my_thread_group_empty(void);
 #define __rcu_dereference_check(p, c, space) \
         ({ \
                 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
-                rcu_lockdep_assert(c); \
+                rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
+                                      " usage"); \
                 rcu_dereference_sparse(p, space); \
                 smp_read_barrier_depends(); \
                 ((typeof(*p) __force __kernel *)(_________p1)); \
         })
 #define __rcu_dereference_protected(p, c, space) \
         ({ \
-                rcu_lockdep_assert(c); \
+                rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
+                                      " usage"); \
                 rcu_dereference_sparse(p, space); \
                 ((typeof(*p) __force __kernel *)(p)); \
         })
@@ -359,7 +373,9 @@ extern int rcu_my_thread_group_empty(void);
 #define __rcu_dereference_index_check(p, c) \
         ({ \
                 typeof(p) _________p1 = ACCESS_ONCE(p); \
-                rcu_lockdep_assert(c); \
+                rcu_lockdep_assert(c, \
+                                   "suspicious rcu_dereference_index_check()" \
+                                   " usage"); \
                 smp_read_barrier_depends(); \
                 (_________p1); \
         })