[PATCH RFC 16/24] srcu: Support Clang's capability analysis

[Marco Elver <elver@google.com>]

Add support for Clang's capability analysis for SRCU.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/srcu.h                          | 61 +++++++++++++------
 lib/test_capability-analysis.c                | 24 ++++++++
 3 files changed, 66 insertions(+), 21 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 73dd28a23b11..3766ac466470 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -86,7 +86,7 @@ Supported Kernel Primitives
 
 Currently the following synchronization primitives are supported:
 `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
-`bit_spinlock`, RCU.
+`bit_spinlock`, RCU, SRCU (`srcu_struct`).
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index d7ba46e74f58..560310643c54 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -21,7 +21,7 @@
 #include <linux/workqueue.h>
 #include <linux/rcu_segcblist.h>
 
-struct srcu_struct;
+struct_with_capability(srcu_struct);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -60,14 +60,14 @@ int init_srcu_struct(struct srcu_struct *ssp);
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
 		void (*func)(struct rcu_head *head));
 void cleanup_srcu_struct(struct srcu_struct *ssp);
-int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
+int __srcu_read_lock(struct srcu_struct *ssp) __acquires_shared(ssp);
+void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 #ifdef CONFIG_TINY_SRCU
 #define __srcu_read_lock_lite __srcu_read_lock
 #define __srcu_read_unlock_lite __srcu_read_unlock
 #else // #ifdef CONFIG_TINY_SRCU
-int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases(ssp);
+int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires_shared(ssp);
+void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 #endif // #else // #ifdef CONFIG_TINY_SRCU
 void synchronize_srcu(struct srcu_struct *ssp);
 
@@ -110,14 +110,16 @@ static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned
 }
 
 #ifdef CONFIG_NEED_SRCU_NMI_SAFE
-int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
+int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires_shared(ssp);
+void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 #else
 static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	return __srcu_read_lock(ssp);
 }
 static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
+	__releases_shared(ssp)
 {
 	__srcu_read_unlock(ssp, idx);
 }
@@ -189,6 +191,14 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+/*
+ * No-op helper to denote that ssp must be held. Because SRCU-protected pointers
+ * should still be marked with __rcu_guarded, and we do not want to mark them
+ * with __var_guarded_by(ssp) as it would complicate annotations for writers, we
+ * choose the following strategy: srcu_dereference_check() calls this helper
+ * that checks that the passed ssp is held, and then fake-acquires 'RCU'.
+ */
+static inline void __srcu_read_lock_must_hold(const struct srcu_struct *ssp) __must_hold_shared(ssp) { }
 
 /**
  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
@@ -202,9 +212,15 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
  * to 1.  The @c argument will normally be a logical expression containing
  * lockdep_is_held() calls.
  */
-#define srcu_dereference_check(p, ssp, c) \
-	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
-				(c) || srcu_read_lock_held(ssp), __rcu)
+#define srcu_dereference_check(p, ssp, c)					\
+({										\
+	__srcu_read_lock_must_hold(ssp);					\
+	__acquire_shared_cap(RCU);						\
+	__auto_type __v = __rcu_dereference_check((p), __UNIQUE_ID(rcu),	\
+				(c) || srcu_read_lock_held(ssp), __rcu);	\
+	__release_shared_cap(RCU);						\
+	__v;									\
+})
 
 /**
  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
@@ -247,7 +263,8 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
  * invoke srcu_read_unlock() from one task and the matching srcu_read_lock()
  * from another.
  */
-static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_read_lock(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -274,7 +291,8 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
  * where RCU is watching, that is, from contexts where it would be legal
  * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
  */
-static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_read_lock_lite(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -295,7 +313,8 @@ static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
  * then none of the other flavors may be used, whether before, during,
  * or after.
  */
-static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -307,7 +326,8 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
 
 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
 static inline notrace int
-srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
+srcu_read_lock_notrace(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -337,7 +357,8 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
  * Calls to srcu_down_read() may be nested, similar to the manner in
  * which calls to down_read() may be nested.
  */
-static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_down_read(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	WARN_ON_ONCE(in_nmi());
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
@@ -352,7 +373,7 @@ static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
  * Exit an SRCU read-side critical section.
  */
 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
@@ -368,7 +389,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
  * Exit a light-weight SRCU read-side critical section.
  */
 static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
@@ -384,7 +405,7 @@ static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
  * Exit an SRCU read-side critical section, but in an NMI-safe manner.
  */
 static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
@@ -394,7 +415,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 
 /* Used by tracing, cannot be traced and cannot call lockdep. */
 static inline notrace void
-srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
+srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases_shared(ssp)
 {
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	__srcu_read_unlock(ssp, idx);
@@ -409,7 +430,7 @@ srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
  * the same context as the maching srcu_down_read().
  */
 static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	WARN_ON_ONCE(in_nmi());
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index f5a1dda6ca38..8bc8c3e6cb5c 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -10,6 +10,7 @@
 #include <linux/rcupdate.h>
 #include <linux/seqlock.h>
 #include <linux/spinlock.h>
+#include <linux/srcu.h>
 
 /*
  * Test that helper macros work as expected.
@@ -345,3 +346,26 @@ static void __used test_rcu_assert_variants(void)
 	lockdep_assert_in_rcu_read_lock_sched();
 	wants_rcu_held_sched();
 }
+
+struct test_srcu_data {
+	struct srcu_struct srcu;
+	long __rcu_guarded *data;
+};
+
+static void __used test_srcu(struct test_srcu_data *d)
+{
+	init_srcu_struct(&d->srcu);
+
+	int idx = srcu_read_lock(&d->srcu);
+	long *data = srcu_dereference(d->data, &d->srcu);
+	(void)data;
+	srcu_read_unlock(&d->srcu, idx);
+
+	rcu_assign_pointer(d->data, NULL);
+}
+
+static void __used test_srcu_guard(struct test_srcu_data *d)
+{
+	guard(srcu)(&d->srcu);
+	(void)srcu_dereference(d->data, &d->srcu);
+}
-- 
2.48.1.502.g6dc24dfdaf-goog