[PATCH tip/core/rcu 0/7] Lockdep-RCU updates for v5.11

[PATCH tip/core/rcu 0/7] Lockdep-RCU updates for v5.11

[Paul E. McKenney]

Hello!

This series simplifies use of the lockdep-RCU API, all courtesy of
Jakub Kicinski:

1.	Un-hide lockdep_tasklist_lock_is_held() for !LOCKDEP.

2.	Un-hide RCU lockdep maps for !LOCKDEP.

3.	Un-hide networking lockdep_sock_is_held() for !LOCKDEP.

4.	Remove broken definitions in sched and un-hide for !LOCKDEP.

5.	Use a more appropriate lockdep helper in SRCU.

6.	Provide dummy forward declaration of *_is_held() helpers.

7.	Prevent RCU_LOCKDEP_WARN() from swallowing the condition.

						Thanx, Paul

------------------------------------------------------------------------

 include/linux/lockdep.h        |    6 ++++++
 include/linux/rcupdate.h       |   11 ++++++-----
 include/linux/rcupdate_trace.h |    4 ++--
 include/linux/sched/task.h     |    2 --
 include/net/sch_generic.h      |   12 ------------
 include/net/sock.h             |    2 --
 kernel/rcu/srcutree.c          |    2 +-
 7 files changed, 15 insertions(+), 24 deletions(-)

[PATCH tip/core/rcu 1/7] sched: Un-hide lockdep_tasklist_lock_is_held() for !LOCKDEP

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

Currently, variables used only within lockdep expressions are flagged as
unused, requiring that these variables' declarations be decorated with
either #ifdef or __maybe_unused.  This results in ugly code.  This commit
therefore causes the lockdep_tasklist_lock_is_held() function to be
visible even when lockdep is not enabled, thus removing the need for
these decorations.  This approach further relies on dead-code elimination
to remove any references to functions or variables that are not available
in non-lockdep kernels.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/sched/task.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 85fb2f3..c0f71f2 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -47,9 +47,7 @@ extern spinlock_t mmlist_lock;
 extern union thread_union init_thread_union;
 extern struct task_struct init_task;
 
-#ifdef CONFIG_PROVE_RCU
 extern int lockdep_tasklist_lock_is_held(void);
-#endif /* #ifdef CONFIG_PROVE_RCU */
 
 extern asmlinkage void schedule_tail(struct task_struct *prev);
 extern void init_idle(struct task_struct *idle, int cpu);
-- 
2.9.5

[PATCH tip/core/rcu 2/7] rcu: Un-hide lockdep maps for !LOCKDEP

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

Currently, variables used only within lockdep expressions are flagged as
unused, requiring that these variables' declarations be decorated with
either #ifdef or __maybe_unused.  This results in ugly code.  This commit
therefore causes the RCU lock maps to be visible even when lockdep is not
enabled, thus removing the need for these decorations.  This approach
further relies on dead-code elimination to remove any references to
functions or variables that are not available in non-lockdep kernels.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/rcupdate.h       | 9 +++++----
 include/linux/rcupdate_trace.h | 4 ++--
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 6cdd015..f9533bb 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -241,6 +241,11 @@ bool rcu_lockdep_current_cpu_online(void);
 static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
 
+extern struct lockdep_map rcu_lock_map;
+extern struct lockdep_map rcu_bh_lock_map;
+extern struct lockdep_map rcu_sched_lock_map;
+extern struct lockdep_map rcu_callback_map;
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 static inline void rcu_lock_acquire(struct lockdep_map *map)
@@ -253,10 +258,6 @@ static inline void rcu_lock_release(struct lockdep_map *map)
 	lock_release(map, _THIS_IP_);
 }
 
-extern struct lockdep_map rcu_lock_map;
-extern struct lockdep_map rcu_bh_lock_map;
-extern struct lockdep_map rcu_sched_lock_map;
-extern struct lockdep_map rcu_callback_map;
 int debug_lockdep_rcu_enabled(void);
 int rcu_read_lock_held(void);
 int rcu_read_lock_bh_held(void);
diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
index 3e7919f..86c8f6c 100644
--- a/include/linux/rcupdate_trace.h
+++ b/include/linux/rcupdate_trace.h
@@ -11,10 +11,10 @@
 #include <linux/sched.h>
 #include <linux/rcupdate.h>
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-
 extern struct lockdep_map rcu_trace_lock_map;
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
 static inline int rcu_read_lock_trace_held(void)
 {
 	return lock_is_held(&rcu_trace_lock_map);
-- 
2.9.5

[PATCH tip/core/rcu 3/7] net: Un-hide lockdep_sock_is_held() for !LOCKDEP

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

Currently, variables used only within lockdep expressions are flagged
as unused, requiring that these variables' declarations be decorated
with either #ifdef or __maybe_unused.  This results in ugly code.
This commit therefore causes the lockdep_sock_is_held() function to be
visible even when lockdep is not enabled, thus removing the need for
these decorations.  This approach further relies on dead-code elimination
to remove any references to functions or variables that are not available
in non-lockdep kernels.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/net/sock.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index a5c6ae7..198d548 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1566,13 +1566,11 @@ do {									\
 	lockdep_init_map(&(sk)->sk_lock.dep_map, (name), (key), 0);	\
 } while (0)
 
-#ifdef CONFIG_LOCKDEP
 static inline bool lockdep_sock_is_held(const struct sock *sk)
 {
 	return lockdep_is_held(&sk->sk_lock) ||
 	       lockdep_is_held(&sk->sk_lock.slock);
 }
-#endif
 
 void lock_sock_nested(struct sock *sk, int subclass);
 
-- 
2.9.5

[PATCH tip/core/rcu 4/7] net: sched: Remove broken definitions and un-hide for !LOCKDEP

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

Currently, variables used only within lockdep expressions are flagged as
unused, requiring that these variables' declarations be decorated with
either #ifdef or __maybe_unused.  This results in ugly code.  This commit
therefore causes the full definitions of the lockdep_tcf_chain_is_locked()
and lockdep_tcf_proto_is_locked() functions to be visible even when
lockdep is not enabled, thus removing the need for the previous empty
functions that were provided in non-lockdep kernels.  This approach
further relies on dead-code elimination to remove any references to
functions or variables that are not available in non-lockdep kernels.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
--
CC: jhs@mojatatu.com
CC: xiyou.wangcong@gmail.com
CC: jiri@resnulli.us
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/net/sch_generic.h | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index d8fd867..749db62 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -435,7 +435,6 @@ struct tcf_block {
 	struct mutex proto_destroy_lock; /* Lock for proto_destroy hashtable. */
 };
 
-#ifdef CONFIG_PROVE_LOCKING
 static inline bool lockdep_tcf_chain_is_locked(struct tcf_chain *chain)
 {
 	return lockdep_is_held(&chain->filter_chain_lock);
@@ -445,17 +444,6 @@ static inline bool lockdep_tcf_proto_is_locked(struct tcf_proto *tp)
 {
 	return lockdep_is_held(&tp->lock);
 }
-#else
-static inline bool lockdep_tcf_chain_is_locked(struct tcf_block *chain)
-{
-	return true;
-}
-
-static inline bool lockdep_tcf_proto_is_locked(struct tcf_proto *tp)
-{
-	return true;
-}
-#endif /* #ifdef CONFIG_PROVE_LOCKING */
 
 #define tcf_chain_dereference(p, chain)					\
 	rcu_dereference_protected(p, lockdep_tcf_chain_is_locked(chain))
-- 
2.9.5

[PATCH tip/core/rcu 5/7] srcu: Use a more appropriate lockdep helper

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

The lockdep_is_held() macro is defined as:

 #define lockdep_is_held(lock)		lock_is_held(&(lock)->dep_map)

This hides away the dereference, so that builds with !LOCKDEP don't break.
This works in current kernels because the RCU_LOCKDEP_WARN() eliminates
its condition at preprocessor time in !LOCKDEP kernels.  However, later
patches in this series will cause the compiler to see this condition even
in !LOCKDEP kernels.  This commit prepares for this upcoming change by
switching from lock_is_held() to lockdep_is_held().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
--
CC: jiangshanlai@gmail.com
CC: paulmck@kernel.org
CC: josh@joshtriplett.org
CC: rostedt@goodmis.org
CC: mathieu.desnoyers@efficios.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index c13348e..6cd6fa2 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -906,7 +906,7 @@ static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
 {
 	struct rcu_synchronize rcu;
 
-	RCU_LOCKDEP_WARN(lock_is_held(&ssp->dep_map) ||
+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
 			 lock_is_held(&rcu_bh_lock_map) ||
 			 lock_is_held(&rcu_lock_map) ||
 			 lock_is_held(&rcu_sched_lock_map),
-- 
2.9.5

[PATCH tip/core/rcu 6/7] lockdep: Provide dummy forward declaration of *_is_held() helpers

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

When CONFIG_LOCKDEP is not set, lock_is_held() and lockdep_is_held()
are not declared or defined.  This forces all callers to use #ifdefs
around these checks.

Recent RCU changes added a lot of lockdep_is_held() calls inside
rcu_dereference_protected().  This macro hides its argument on !LOCKDEP
builds, which can lead to false-positive unused-variable warnings.

This commit therefore provides forward declarations of lock_is_held()
and lockdep_is_held() but without defining them.  This way callers
(including those internal to RCU) can keep them visible to the compiler
on !LOCKDEP builds and instead depend on dead code elimination to remove
the references, which in turn prevents the linker from complaining about
the lack of the corresponding function definitions.

[ paulmck: Apply Peter Zijlstra feedback on "extern". ]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
--
CC: peterz@infradead.org
CC: mingo@redhat.com
CC: will@kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/lockdep.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index f559487..ccc3ce6 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -375,6 +375,12 @@ static inline void lockdep_unregister_key(struct lock_class_key *key)
 
 #define lockdep_depth(tsk)	(0)
 
+/*
+ * Dummy forward declarations, allow users to write less ifdef-y code
+ * and depend on dead code elimination.
+ */
+extern int lock_is_held(const void *);
+extern int lockdep_is_held(const void *);
 #define lockdep_is_held_type(l, r)		(1)
 
 #define lockdep_assert_held(l)			do { (void)(l); } while (0)
-- 
2.9.5

[PATCH tip/core/rcu 7/7] rcu: Prevent RCU_LOCKDEP_WARN() from swallowing the condition

[paulmck]

From: Jakub Kicinski <kuba@kernel.org>

We run into a unused variable warning in bridge code when variable is
only used inside the condition of rcu_dereference_protected().

 #define mlock_dereference(X, br) \
	rcu_dereference_protected(X, lockdep_is_held(&br->multicast_lock))

Since on builds with CONFIG_PROVE_RCU=n rcu_dereference_protected()
compiles to nothing the compiler doesn't see the variable use.

This commit therefore prevents this warning by adding the condition as
dead code.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
--
CC: paulmck@kernel.org
CC: josh@joshtriplett.org
CC: rostedt@goodmis.org
CC: mathieu.desnoyers@efficios.com
CC: joel@joelfernandes.org
CC: jiangshanlai@gmail.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/rcupdate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f9533bb..de08264 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -328,7 +328,7 @@ static inline void rcu_preempt_sleep_check(void) { }
 
 #else /* #ifdef CONFIG_PROVE_RCU */
 
-#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
+#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
 #define rcu_sleep_check() do { } while (0)
 
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
-- 
2.9.5