Merge branch 'kcsan' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into locking/core

Pull KCSAN updates for v5.10 from Paul E. McKenney:

 - Improve kernel messages.

 - Be more permissive with bitops races under KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=y.

 - Optimize debugfs stat counters.

 - Introduce the instrument_*read_write() annotations, to provide a
   finer description of certain ops - using KCSAN's compound instrumentation.
   Use them for atomic RNW and bitops, where appropriate.
   Doing this might find new races.
   (Depends on the compiler having tsan-compound-read-before-write=1 support.)

 - Support atomic built-ins, which will help certain architectures, such as s390.

 - Misc enhancements and smaller fixes.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Author: ingomolnar

include/asm-generic/atomic-instrumented.h

@@ -67,7 +67,7 @@ static inline void change_bit(long nr, volatile unsigned long *addr)
  */
 static inline bool test_and_set_bit(long nr, volatile unsigned long *addr)
 {
-	instrument_atomic_write(addr + BIT_WORD(nr), sizeof(long));
+	instrument_atomic_read_write(addr + BIT_WORD(nr), sizeof(long));
 	return arch_test_and_set_bit(nr, addr);
 }
 
@@ -80,7 +80,7 @@ static inline bool test_and_set_bit(long nr, volatile unsigned long *addr)
  */
 static inline bool test_and_clear_bit(long nr, volatile unsigned long *addr)
 {
-	instrument_atomic_write(addr + BIT_WORD(nr), sizeof(long));
+	instrument_atomic_read_write(addr + BIT_WORD(nr), sizeof(long));
 	return arch_test_and_clear_bit(nr, addr);
 }
 
@@ -93,7 +93,7 @@ static inline bool test_and_clear_bit(long nr, volatile unsigned long *addr)
  */
 static inline bool test_and_change_bit(long nr, volatile unsigned long *addr)
 {
-	instrument_atomic_write(addr + BIT_WORD(nr), sizeof(long));
+	instrument_atomic_read_write(addr + BIT_WORD(nr), sizeof(long));
 	return arch_test_and_change_bit(nr, addr);
 }
 

include/asm-generic/bitops/instrumented-atomic.h

@@ -52,7 +52,7 @@ static inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
  */
 static inline bool test_and_set_bit_lock(long nr, volatile unsigned long *addr)
 {
-	instrument_atomic_write(addr + BIT_WORD(nr), sizeof(long));
+	instrument_atomic_read_write(addr + BIT_WORD(nr), sizeof(long));
 	return arch_test_and_set_bit_lock(nr, addr);
 }
 

include/asm-generic/bitops/instrumented-lock.h

@@ -58,6 +58,30 @@ static inline void __change_bit(long nr, volatile unsigned long *addr)
 	arch___change_bit(nr, addr);
 }
 
+static inline void __instrument_read_write_bitop(long nr, volatile unsigned long *addr)
+{
+	if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC)) {
+		/*
+		 * We treat non-atomic read-write bitops a little more special.
+		 * Given the operations here only modify a single bit, assuming
+		 * non-atomicity of the writer is sufficient may be reasonable
+		 * for certain usage (and follows the permissible nature of the
+		 * assume-plain-writes-atomic rule):
+		 * 1. report read-modify-write races -> check read;
+		 * 2. do not report races with marked readers, but do report
+		 *    races with unmarked readers -> check "atomic" write.
+		 */
+		kcsan_check_read(addr + BIT_WORD(nr), sizeof(long));
+		/*
+		 * Use generic write instrumentation, in case other sanitizers
+		 * or tools are enabled alongside KCSAN.
+		 */
+		instrument_write(addr + BIT_WORD(nr), sizeof(long));
+	} else {
+		instrument_read_write(addr + BIT_WORD(nr), sizeof(long));
+	}
+}
+
 /**
  * __test_and_set_bit - Set a bit and return its old value
  * @nr: Bit to set
@@ -68,7 +92,7 @@ static inline void __change_bit(long nr, volatile unsigned long *addr)
  */
 static inline bool __test_and_set_bit(long nr, volatile unsigned long *addr)
 {
-	instrument_write(addr + BIT_WORD(nr), sizeof(long));
+	__instrument_read_write_bitop(nr, addr);
 	return arch___test_and_set_bit(nr, addr);
 }
 
@@ -82,7 +106,7 @@ static inline bool __test_and_set_bit(long nr, volatile unsigned long *addr)
  */
 static inline bool __test_and_clear_bit(long nr, volatile unsigned long *addr)
 {
-	instrument_write(addr + BIT_WORD(nr), sizeof(long));
+	__instrument_read_write_bitop(nr, addr);
 	return arch___test_and_clear_bit(nr, addr);
 }
 
@@ -96,7 +120,7 @@ static inline bool __test_and_clear_bit(long nr, volatile unsigned long *addr)
  */
 static inline bool __test_and_change_bit(long nr, volatile unsigned long *addr)
 {
-	instrument_write(addr + BIT_WORD(nr), sizeof(long));
+	__instrument_read_write_bitop(nr, addr);
 	return arch___test_and_change_bit(nr, addr);
 }
 

include/asm-generic/bitops/instrumented-non-atomic.h

@@ -42,6 +42,21 @@ static __always_inline void instrument_write(const volatile void *v, size_t size
 	kcsan_check_write(v, size);
 }
 
+/**
+ * instrument_read_write - instrument regular read-write access
+ *
+ * Instrument a regular write access. The instrumentation should be inserted
+ * before the actual write happens.
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+static __always_inline void instrument_read_write(const volatile void *v, size_t size)
+{
+	kasan_check_write(v, size);
+	kcsan_check_read_write(v, size);
+}
+
 /**
  * instrument_atomic_read - instrument atomic read access
  *
@@ -72,6 +87,21 @@ static __always_inline void instrument_atomic_write(const volatile void *v, size
 	kcsan_check_atomic_write(v, size);
 }
 
+/**
+ * instrument_atomic_read_write - instrument atomic read-write access
+ *
+ * Instrument an atomic read-write access. The instrumentation should be
+ * inserted before the actual write happens.
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+static __always_inline void instrument_atomic_read_write(const volatile void *v, size_t size)
+{
+	kasan_check_write(v, size);
+	kcsan_check_atomic_read_write(v, size);
+}
+
 /**
  * instrument_copy_to_user - instrument reads of copy_to_user
  *

include/linux/instrumented.h

@@ -7,19 +7,13 @@
 #include <linux/compiler_attributes.h>
 #include <linux/types.h>
 
-/*
- * ACCESS TYPE MODIFIERS
- *
- *   <none>: normal read access;
- *   WRITE : write access;
- *   ATOMIC: access is atomic;
- *   ASSERT: access is not a regular access, but an assertion;
- *   SCOPED: access is a scoped access;
- */
-#define KCSAN_ACCESS_WRITE  0x1
-#define KCSAN_ACCESS_ATOMIC 0x2
-#define KCSAN_ACCESS_ASSERT 0x4
-#define KCSAN_ACCESS_SCOPED 0x8
+/* Access types -- if KCSAN_ACCESS_WRITE is not set, the access is a read. */
+#define KCSAN_ACCESS_WRITE	(1 << 0) /* Access is a write. */
+#define KCSAN_ACCESS_COMPOUND	(1 << 1) /* Compounded read-write instrumentation. */
+#define KCSAN_ACCESS_ATOMIC	(1 << 2) /* Access is atomic. */
+/* The following are special, and never due to compiler instrumentation. */
+#define KCSAN_ACCESS_ASSERT	(1 << 3) /* Access is an assertion. */
+#define KCSAN_ACCESS_SCOPED	(1 << 4) /* Access is a scoped access. */
 
 /*
  * __kcsan_*: Always calls into the runtime when KCSAN is enabled. This may be used
@@ -204,6 +198,15 @@ static inline void __kcsan_disable_current(void) { }
 #define __kcsan_check_write(ptr, size)                                         \
 	__kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
 
+/**
+ * __kcsan_check_read_write - check regular read-write access for races
+ *
+ * @ptr: address of access
+ * @size: size of access
+ */
+#define __kcsan_check_read_write(ptr, size)                                    \
+	__kcsan_check_access(ptr, size, KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)
+
 /**
  * kcsan_check_read - check regular read access for races
  *
@@ -221,18 +224,30 @@ static inline void __kcsan_disable_current(void) { }
 #define kcsan_check_write(ptr, size)                                           \
 	kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
 
+/**
+ * kcsan_check_read_write - check regular read-write access for races
+ *
+ * @ptr: address of access
+ * @size: size of access
+ */
+#define kcsan_check_read_write(ptr, size)                                      \
+	kcsan_check_access(ptr, size, KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)
+
 /*
  * Check for atomic accesses: if atomic accesses are not ignored, this simply
  * aliases to kcsan_check_access(), otherwise becomes a no-op.
  */
 #ifdef CONFIG_KCSAN_IGNORE_ATOMICS
-#define kcsan_check_atomic_read(...)	do { } while (0)
-#define kcsan_check_atomic_write(...)	do { } while (0)
+#define kcsan_check_atomic_read(...)		do { } while (0)
+#define kcsan_check_atomic_write(...)		do { } while (0)
+#define kcsan_check_atomic_read_write(...)	do { } while (0)
 #else
 #define kcsan_check_atomic_read(ptr, size)                                     \
 	kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC)
 #define kcsan_check_atomic_write(ptr, size)                                    \
 	kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE)
+#define kcsan_check_atomic_read_write(ptr, size)                               \
+	kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND)
 #endif
 
 /**