srcu: Create CPP macros for normal and NMI-safe SRCU readers

This commit creates SRCU_READ_FLAVOR_NORMAL and SRCU_READ_FLAVOR_NMI
C-preprocessor macros for srcu_read_lock() and srcu_read_lock_nmisafe(),
respectively.  These replace the old true/false values that were
previously passed to srcu_check_read_flavor().  In addition, the
srcu_check_read_flavor() function itself requires a bit of rework to
handle bitmasks instead of true/false values.

Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Neeraj Upadhyay <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>

Author: paulmckrcu

include/linux/srcu.h

@@ -176,10 +176,6 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
-#define SRCU_NMI_UNKNOWN	0x0
-#define SRCU_NMI_UNSAFE		0x1
-#define SRCU_NMI_SAFE		0x2
-
 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
 void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
 #else
@@ -247,7 +243,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;
 
-	srcu_check_read_flavor(ssp, false);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	retval = __srcu_read_lock(ssp);
 	srcu_lock_acquire(&ssp->dep_map);
 	return retval;
@@ -268,7 +264,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
 {
 	int retval;
 
-	srcu_check_read_flavor(ssp, true);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
 	retval = __srcu_read_lock_nmisafe(ssp);
 	rcu_try_lock_acquire(&ssp->dep_map);
 	return retval;
@@ -280,7 +276,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;
 
-	srcu_check_read_flavor(ssp, false);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	retval = __srcu_read_lock(ssp);
 	return retval;
 }
@@ -309,7 +305,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
 {
 	WARN_ON_ONCE(in_nmi());
-	srcu_check_read_flavor(ssp, false);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	return __srcu_read_lock(ssp);
 }
 
@@ -324,7 +320,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
 	__releases(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
-	srcu_check_read_flavor(ssp, false);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	srcu_lock_release(&ssp->dep_map);
 	__srcu_read_unlock(ssp, idx);
 }
@@ -340,7 +336,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 	__releases(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
-	srcu_check_read_flavor(ssp, true);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
 	rcu_lock_release(&ssp->dep_map);
 	__srcu_read_unlock_nmisafe(ssp, idx);
 }
@@ -349,7 +345,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 static inline notrace void
 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
 {
-	srcu_check_read_flavor(ssp, false);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	__srcu_read_unlock(ssp, idx);
 }
 
@@ -366,7 +362,7 @@ static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	WARN_ON_ONCE(in_nmi());
-	srcu_check_read_flavor(ssp, false);
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	__srcu_read_unlock(ssp, idx);
 }
 

include/linux/srcutree.h

@@ -43,6 +43,10 @@ struct srcu_data {
 	struct srcu_struct *ssp;
 };
 
+/* Values for ->srcu_reader_flavor. */
+#define SRCU_READ_FLAVOR_NORMAL	0x1		// srcu_read_lock().
+#define SRCU_READ_FLAVOR_NMI	0x2		// srcu_read_lock_nmisafe().
+
 /*
  * Node in SRCU combining tree, similar in function to rcu_data.
  */

kernel/rcu/srcutree.c

@@ -463,7 +463,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
 			mask = mask | READ_ONCE(sdp->srcu_reader_flavor);
 	}
 	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
-		  "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
+		  "Mixed reader flavors for srcu_struct at %ps.\n", ssp);
 	return sum;
 }
 
@@ -703,20 +703,21 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  */
 void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
 {
-	int reader_flavor_mask = 1 << read_flavor;
-	int old_reader_flavor_mask;
+	int old_read_flavor;
 	struct srcu_data *sdp;
 
-	/* NMI-unsafe use in NMI is a bad sign */
-	WARN_ON_ONCE(!read_flavor && in_nmi());
+	/* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */
+	WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi());
+	WARN_ON_ONCE(read_flavor & (read_flavor - 1));
+
 	sdp = raw_cpu_ptr(ssp->sda);
-	old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor);
-	if (!old_reader_flavor_mask) {
-		old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask);
-		if (!old_reader_flavor_mask)
+	old_read_flavor = READ_ONCE(sdp->srcu_reader_flavor);
+	if (!old_read_flavor) {
+		old_read_flavor = cmpxchg(&sdp->srcu_reader_flavor, 0, read_flavor);
+		if (!old_read_flavor)
 			return;
 	}
-	WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask);
+	WARN_ONCE(old_read_flavor != read_flavor, "CPU %d old state %d new state %d\n", sdp->cpu, old_read_flavor, read_flavor);
 }
 EXPORT_SYMBOL_GPL(srcu_check_read_flavor);
 #endif /* CONFIG_PROVE_RCU */